Is 16GB unified memory sufficient for my workload on a new Mac mini?

For your workflow, 16GB unified memory on the M4 Mac mini should be plenty for several years. The unified memory architecture is efficient, so running Office apps, multiple browser windows, and research tools won’t be an issue.

Migration from your iMac is straightforward with Migration Assistant, either wirelessly or via Time Machine — a Genius Bar visit isn’t necessary unless you prefer in-person support. Overall, this upgrade should feel much faster and smoother than your 2015 iMac.

1. No one ever regretted buying more RAM than they thought they needed. Buy as much as your budget allows. You can always buy external drives if you need more storage but, these days, it's hard (sometimes impossible) to add more RAM.
2. I bought a new computer about a year ago. Transferring over was very easy. I used MIgration Assistant. Given that it takes some time and schlepping a iMac to the Apple Store would be annoying, I'd at least give it a try yourself.

Transfer to a new Mac with Migration Assistant - Apple Support

Check to see how much disk space your current iMac is using...?

A 256GB storage drive can fill up pretty fast and cause serious problems.

If it's in the budget, I recommend going with the 24GB Unified Memory / 512GB Storage Mac mini.

Buy Mac mini - Apple

I agree with Idris, that Migrating to a new Mac is fairly straight forward and easy.

The fastest way to migrate, is from your Time Machine or clone backup.

Transfer to a new Mac with Migration Assistant - Apple Support

I agree wholeheartedly with Servant of Cats about the minimum storage which should be ordered. I have a 16 GB RAM M4 Mini with a 1 TB SSD. I would not get any Mac with less than 1 TB. Why, because as you've been told it can fill up quickly with music and photos. Also if you're coming from a Mac with more than 256 user files you can't use Migration Assistant to move those files to the new Mini. Also it's good practice to maintain a minimum of 80-100 GB of free space to facilitate optimal system and application performance.

With the 16 GB of RAM I can open and edit a huge 500+ Mb Photoshop file with little problem. I created a file that large just to test different applications. All of my photos are 5 Mb or less in size so no problem there.

Also have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac? If you have that may be part of the problem for you 2015 iMac problems. Be sure to remove them and all their supporting files before moving your user files to your new Mini.

As for your 2015 iMac it sounds like a drive is beginning to go. Does it have a Fusion drive? If so the HDD portion is the most likely to be failing. That can be circumvented, if that's the case, by getting an external SSD, cloning you boot drive to it and then boot and run from the external SSD. I did that for one of my older iMac a while ago.

Just some food for thought.

steper1 wrote:

Since my work consists of running MSOffice apps (for Mac) about 90% of the time, I intend to buy the Apple 2024 Mac mini with the M4 chip (10‑core CPU & 10‑core GPU), 16GB Unified Memory. I already have an iCloud Drive account for my business records, so the 256GB SSD Storage should be enough.

I would not recommend getting any Mac with only 256 GB of internal storage, unless you are very sure that your needs are very minimal and will not grow.

The 512 GB SSD on my Mac is already about half full. This does include ~40 GB of photos, but it doesn't include any music, movies, or TV shows (those libraries are on an external drive).

2 - Is porting my iMac over to the mini as simple a process as it has been previously when I've upgraded to new iMac's in the past, or should I set an appointment with the Genius Bar and take my iMac there and have them do it?

Assuming that your new Mac's internal drive is big enough to hold the data from your old Mac, just make an up-to-date backup of your old Mac on an external drive.

This backup can be a Time Machine backup – or a bootable clone backup ("startup disk") prepared with the aid of Carbon Copy Cloner or SuperDuper! Whatever you have on hand, as long as it is current.

Transfer the backup drive to the new Mac and point Migration Assistant at it. (You'll probably need something like Apple's USB-C to USB adapter to overcome the difference in USB connector types.)

Congrats on getting your money out of that 2015.

16GB should be fine for anyone planning to replace every 3-5 years, but I don't think it will stand the test of time for a long term owner. If you are hoping the mini will last as long as your old iMac I would suggest stepping up to 24GB RAM.

My MB Air has 16GB and I generally have a word processor, mail, a browser, and several utility apps running at the same time. I also frequently boot up a graphic editor. In short, 16GB is plenty for today but I also have a mini with 32GB so my bets are covered. (I’ve always tended to buy a desktop with longevity in mind but upgrade notebooks more frequently) What I’m not so sure about though is your choice of a 256GB drive. My personal feeling is that data belongs on my personal hard drive, the cloud is for sharing but that’s just me. If you also have all your business data backed up on a hard drive, add a second hard drive for backup. If not, get the iCloud data on a local drive or two. Back when I was doing tech consulting I had 2 clients who went out of business because they lost their data due to drive failure. Until I retired I kept one backup drive at home and one in my office. Today my neighbor and I are each other’s safe repository

Servant of Cats wrote:

....

This backup can be a Time Machine backup – or a bootable clone backup ("startup disk") prepared with the aid of Carbon Copy Cloner or SuperDuper! ....

FYI, you can restore from a non-bootable CCC clone, i.e. data volume clone. I have done this multiple times and have had zero issues for several years now.

I have a 2017 iMac and my basic M4 mini (16GB RAM) is 3 times faster . . . there is no comparison. (My M2 mini 8GB RAM is also 2 times faster than the iMac.

You will not know what hit you . . . it is light years ahead (slight hyperbole).

The 256GB SSD is completely immaterial . . . to double its size will cost you £200 for which you could buy a 2TB NVMe SSD and still have a huge chunk of the moolah leftover.

Just to add to @den.thed, when Migration Assistant does its thing, it only works on the "data" volume anyway. This changed quite a while ago when Time Machine no longer backed up the entire system and only backed up the Data volume which coincided with Apple switching to the sealed system volume.

i think 16gb ram should be enough for you but if you can then you might get 32gb ram instead

Yes, I have also used non-bootable CCC clones more than 6 times in the last 10 years.

That sounds like a solid plan, assuming you are planing on an SSD for the Hub. The only suggested change would be separate drives for daily functionality and Time Machine. (Tip: If want to backup both the internal and expansion drives to Time Machine the external drive/hub will need to be formatted as APFS, not EXFAT.)

For old iMacs, slow system startup times often indicate drive trouble. I think a late 2015 is too old to try and fix for work use, but if you have any interest in trying to save the old iMac for personal/guest use and ordered a USB SSD separate from the hub for your new Time Machine then you could try first reinstalling MacOS onto the new SSD as a quick external startup drive test for the old iMac. If it works you know how to fix the iMac. If the iMac is still slow all you have lost is a the time tinkering. How to use an external storage device as a Mac startup disk - Apple Support