My 2015 15" MBP is also still kickin, is/was an absolutely fabulous unit. Was my work machine for 3-4 years, and now another almost-6 years as my personal laptop. My personal use case is obviously not very demanding but it's only now starting to really show its age.
I also have a M1 from work that is absolutely wonderful, but I think it's time for me to upgrade the 2015 with one of these new M4s.
Honestly, my Thinkpad from 2015 was still used in my family until recently. The battery was pretty bad, same as on my 2015 MBP, but other than that, I put Fedora on it, and it was still really fast.
Longevity is not only a thing of MBPs. OTOH, IIRC, some 2017-2019 MBPs (before the Mx switch) were terrible for longevity, given their problematic keyboard.
I also have a M1 from work that is absolutely wonderful, but I think it's time for me to upgrade the 2015 with one of these new M4s.
The longevity of Macbooks is insanely good.