Hi,
I also tried Parallels 15 on my MBP 2017 (first time I bought Parallels on day one!

) from my bootcamp partition and it works indeed but for now quite slower than the "old" Mac version.
I also did only undock - flyby -dock but in my case I manage to have 20-30 FPS on low settings and HD resolution, quite lower than what I used to have and what I can achieve in bootcamp.
I am still in Mojave though, most probably the new Metal version in Catalina should improve everything massively (in fact Parallels mentions explicitly E

compatibility with Catalina)
These are indeed great news (I tried to Bootcamp but am somehow too lazy to just reboot only for a short trip in space...), if only Frontier would now use the new Apple game framework natively.....
I would probably end buying an eGPU!
Rad