What specs are you running?
I have a similar question, have put Affinity on an old machine to play/learn - it runs but very laggy (and crashed a few times) if I have too many images open at once. Mostly I shoot RAW and like doing HDR so thats kind of demanding
This device is c10 years old with low spec i3 M380 and 4GB of memory (mostly the kids use for the internet) but with a modern SSD drive. I think low memory is my issue, esp with HDRs
PS - you say you are running Win7 x64, is that on an OEM machine (ie did the device come with Win 7 installed)? If so you can probably move to Win10 for free, that's what I did with this old laptop