I have this issue with other games. For me it was a conflict between the older game which was limited to 2GB RAM (and thus ignored the rest of the GBs) and an anti-virus that liked to check every file whenever it was accessed.
I ended up unplugging the computer from the Internet, disabling the Anti-Virus memory hog, and using that computer solely for gaming offline. That solved my problem.
Maybe someone else has better advice more suited to your system, but it seems to me that Windows 10 works a lot differently and uses more RAM than Vista did. Also, as far as I know, Windows 10 is not particularly keen on being backwards-compatible.