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.