Most of the iMacs / Minis run fine initially but turn into dogs after one or two OS X updates... if i was a conspiracy theory guy I'd say they build in obsolescence with each OS release, but then again they don't release new models, so....
My 2014 mini which would run Photoshop Ok initially now takes a minute to open it.... and there is nothing newer to buy....
I've re-installed it from scratch and it make surprisingly little difference for all the work... you have to perform major surgery (see below) to add memory and SSD, that helps but its still an older processor...
Just saying it would not kill them to refresh desktops more often than every 2 or 3 years... "buy a laptop" is not the solution for all... Again, I'm fine with it *if* that's the way they are going, I need to switch to Windoze then - but I'd like to know for sure... i have a track record for buying Macs 2 weeks before a new model comes out...