What do you dislike about the OS? Presumably it's running macOS Mojave?
I am sure I will think of some other annoyances. I've kept a 2012 MBP on Sierra, and love that machine far more, eg. keyboard is actually good and is quiet, real function keys, real ports as found on every other device in the universe, ability to use my audio interface, network ports etc etc
Edit. It does to a degree. Firefox takes on the dark theme but everything else seems fine so far.
Have tried everything short of a complete reformat - NVRAM, SMC reset. Nothing in activity monitor gives me any clues either.
I even rolled back to High Sierra to check my sanity. No crazy fan spin. Reinstalled Mojave --> crazy fan spin.