I see. My virtual machine was very slow too and LoLK had extremely low FPS obviously, but after I adjusted some settings etc., the OS in general works faster but LoLK is still the same (I thought it'd be at least a little bit better too). Also, I installed an English patch, the one that's called Touhou Community Reliant Automatic Patcher, perhaps it might also cause problems. However now I'm inclined that VM is the main reason anyway.
By the way, I've tried running TH15 with Wine. It didn't work on MacOS Catalina (my host OS) but everything was alright on another computer with an earlier version of the OS. In general I think it's the optimal solution for Mac and Linux users, I only decided to try a virtual machine because Wine doesn't work on Catalina (this OS doesn't support 32-bit apps anymore).
I used to play Touhou a lot some years ago, I didn't become a very skilled player but enjoyed the games so much. Sad that there is probably no possibility to play them on new Mac, either way. I can still launch Touhou on my VM to go to Music Room and listen to the soundtrack though, thankfully it's brilliant in TH15 ;D
Anyway thank you so much for your answer!
UPD: even on 15FPS it's playable though, very frustrating sometimes but still possible, I even attempted the extra. So this issue is not crucial anymore I suppose