I get this error pretty regularly in 15 too -- probably every 10-20 minutes when I'm doing really heavy beauty work with lots of noise reduction on 8K footage and many (many) nodes, etc. Mostly I'm at 1080p but UHD makes it noticeably worse. This is on the 2 x 1080 Ti / 2080 Ti systems in my signature.
I'm sure there are bugs going on under the hood that are different in 15, but my bet for why this is coming up more often than 14 or 12.5 is because there are just more tools (and more demanding footage) to push Resolve with now. The tools available to really push Resolve 2+ years ago were nothing compared to what we've got now.
It will be nice if they can fix things but the traditional solution still works for material that's too demanding: noise-reduce, export a plate of appropriate size, get back to work using something with less computational overhead.
It would be nice if it all worked in real-time though