the emulator makes the CPU spin at 100% on a 2015 macbook pro...
any ideas how to make it less power hungry?

Open one of three .conf files with a text editor and find the line "cycles="
(I believe it's the shortest named one, but with most options)
Change auto or max or whatever it ways to 20000 or 25000.
That will also decrease screen scrolling speed to something manageable by a human being.

Auto is equivalent to 200000+ cycles btw, absolutely no reason for GoG to use it in most cases.