We have a lot of people at work with 2015 models - and they are SUPER happy. I have the 2018 model with i7 and I can't really see any difference in performance. I love the display, but mostly I use a 27 inch high DPI external screen along with an Apple magic keyboard.
One thing I strongly dislike about the i7 is how hot it can get with long compiles and such. So I think it's time to upgrade to the M1 Pro or Max.
Got the same life out of mine, although the battery swelled up this year. :-/
Didn't bother to look into the cost of replacement as my initial research indicated that they'd want/need to replace the keyboard and upper chassis as well, so probably a $600+ repair. So I opted for a company laptop instead.
Really the only thing that doesn't work well on it to this day is the dreaded Microsoft Teams, which brings the thing to a screeching halt.
Well, plus trying to do more than minimal VM/container use, to be honest.