I mentioned a cheap dedicated server because I'm not sure when quicksync was introduced, if you need to do any transcoding at all an intel macbook will probably catch fire.

and if you haven't already then change the thermal paste. I have a 2015 pro as well and it gets real hot, factory paste can be a crap shoot if it's even making contact in the first place much less after a decade and new paste actually makes a bigger difference in performance than I expected.