I had both and the 2014 was my favorite. Family member still rolls with 2015+Big Sur. The 2014 was the last MacBook Pro to include an nVidia GPU if I recall correctly. I also like the physical TouchPad press instead of the haptic Force Touch. The storage in the 2015 is faster (PCIe 3.0 v. PCIe 2.0 in 2014) but not super noticeable. I will dig up my benchmark results tomorrow as I have a spreadsheet somewhere that has the same tests run on 2012 through 2019 MacBook Pros I’ve owned. It’ll run Big Sur just fine (assuming you aren’t concerned about security updates since Big Sur has about a month to go before Sonoma is released and Big Sur drops off support - and Monterey only buys you one more year of support). Also runs Linux like a champ.