(Message also for your parent) Last week, I saw the writing on the wall. I installed OpenCore-Legacy-Patcher on two MBPs from 2015, updating 12.7 to 13.6. It is a MBP 13" 2015 (early 2016 variant) and a MBP 15" 2015 (late 2015?). Works very well but you need to follow the guide. Both machines are still working well, 'cept for the battery (already replaced on the 13"). Esp the 15" is still in good condition, my wife happily uses it and insists on needing a 15". So a replacement would be expensive.
Can confirm Ventura runs great on a mid-2015 MacBook Pro 15 inch (MacBookPro11,4). Mine has 16gb of RAM and an i7 which probably helps (also added a modern 1tb NVMe drive via an adapter). I use it for a dedicated music production setup and only ever hear fans when installing something or during updates.
My only advice for someone new to OCLP/unfamiliar with Mac boot loader in general (like me one week ago) is that the OCLP boot screen during setup looks very similar to the native MacOS boot picker and went through four different flash drives trying to follow the instructions thinking it wasn't booting properly from the drive. Look closely at the instruction screenshot to distinguish them.
[1] https://dortania.github.io/OpenCore-Legacy-Patcher/INSTALLER...