As a graphic designer and amateur photographer myself, here is my advice.
First, I would probably upgrade to a new machine. I'm impressed that you are able to work on any kind of high-resolution images with your 2015 MBP, especially with only 8gb of RAM. I second the opinion that you want the fastest thing you can afford.
If you're going to get a new MBP, do not skimp on RAM or internal storage. I would also study the chip speeds to help you make a decision--I usually end up getting the middle-of-the-road option, but for this last machine, I went with the Max option because it wasn't that much more expensive. Or maybe I had to get the faster chip to get more RAM?
In my opinion, these three things--RAM, internal storage and chip speed--will give your device the most longevity. Congrats on achieving 10 years with your current setup! I expect you'll keep the next machine for 10 years. Keep in mind that everything these days has some AI component that requires hardware to run. Cameras will only get more capable, producing higher resolution images, and those files will take up space on your internal storage.
I have an MBP M1 Max (2022) with 32gb RAM and it's still very capable. I can have all the Adobe apps running at the same time: Ps, LrC, Ai, InDe, font manager, along with the usual email, browser with bunches of tabs, Excel, and Word docs, and it doesn't lag at all. If I could update the SSD on my current setup, I would be happy, but unfortunately, that's not an option. Right now, larger internal storage is the only reason I'm even thinking about a new machine.
I've never used the OM software, but I did use Nikon's software for a while. Meh. I drank the Adobe kool-aid long ago however, and am a subscription-paying idiot. I love Lightroom Classic's editing interface and its photo organization capabilities. I also use Topaz and Luminar Neo occasionally, both of which have some AI components that run locally, as does the latest version of Photoshop. They are all memory-hungry these days.
I ramble, sorry. Good luck with your decision! I hope I was able to help.