Monterey upgrade for MacBook Pro mid 2015

Welcome but unless the computer has very specific limitations - there should be no reason not to upgrade to the latest version of macOS it Qualifies to run.

As long as the User has a Rescue Plan in place before attempting - things should move forwards .

Tips Monterey Upgrade 

The below points should be consider before attempting the upgrade.

Point # 1 - Does the >>  Computer Qualify for the Monterey upgrade 

Point # 1A - There are reports appearing on the ASC Forums regarding failed installation of Monterey on older Qualifying Apple Computers. In most cases this is related to having a NON Apple Original Internal Drive ?  

The EFI Boot ROM included in Monterey is verifying for Original Apple Drive and if not found , may Balk or fail to upgrade to Monterey. 

Reports indicate the EFI BOOT ROM is Required to Flash the Computer and is a  requirement for a Successful Monterey Installation.

Point # 1B - Caution - jumping over all the newer versions and directly to Big Sur  / Monterey on Qualifying computers is Technically possible - there are those who have attempted and were successful.

Then there are those who attempted and had less than good results.

If this is a Production or Mission Critical Set-up - a more prudent and measure approach is suggested. 

The above is from observations on the Apple Support Community Forums and IMHO

Point # 2 - >> How to upgrade to macOS Monterey

Point # 3 - Empty Space Requirements  >> If upgrading from macOS Sierra or later, your Mac needs 26GB of available storage to upgrade. If upgrading from an earlier release, your Mac needs up to 44GB of available storage. 

Point # 4 - Empty Space afterwards - it is suggested to keep at least 15%  to 20% of the Drive Total Capacity as Empty Space for good operations of the computer and for additional updates to Monterey to download, expand and install.

Point # 5 - The upgrade will require a quick, stable and reliable Internet Connection - preferred method is via Ethernet Connection. 

Point # 6 - If using Wifi - move computer as close to the Access Point / Router and disconnect all other devices connected to Wifi. Want the maximum bandwidth for the computer being upgraded to Monterey

Point # 7 -  Commercial VPNs   should only be used if Mandated by Corporate Head Office for working remotely. Otherwise - ones Privacy and Security touted by the VPN is suspect. 

Point # 8 - If downloading Monterey from behind a VPN it may increase Packet Looses and an incomplete or corrupted Installer.

Point # 9 - AntiVirus Software should be removed as per Developers Instructions. They are unneeded, cause havoc and interfere with the normal operation of the OS including the download and installation of Monterey. 

The Built in Security  is all that is required. 

There are no known Windows-like Viruses in the wild that self replicate and affect macOS because of the underling UNIX  Foundation and Permission Limitation. 

Point # 10 - Disk Cleaners, Optimizers and UnInstaller are not needed. They will often times attempt to Modify, Alter, Remove or Delete elements of the Operating System requiring a Re-Installation.

Point # 11 - Do you have a Rescue Plan In-Place. This comprises having 3 Backups using 2 methods and 1 Off Site incase of Theft, Loss or Natural Disasters. A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS. 

Point # 12 - For addition purposes - two Tested Clones each to separate external drives. This is insurance incase the upgrades goes sideways. At least one Tested Clone and / or Time Machine Backup should be Off - Site

Does my CCC backup have to be bootable for me to restore data from it?

Point # 13 - Are the installed Applications / Extensions compatible with Monterey. Check with the Developer for compatible Apps / extensions. Do they offer updates or upgrades. Same goes for Third Party Drivers for Printer, Scanners etc.