The nature of VMs is that you can assign memory to it. So if your machine is already light, you wouldn't give it much memory to start with, and it'd run (just slower)
Not saying that at all. Saying that if someone says it'll run in 8GB instead of 16GB, or 16 instead of 32, it's possible, but those claims ignore performance. The presence of those statements means absolutely nothing absent of context (for instance, the required performance of a Windows 10 VM isn't the same for someone just testing a site on IE versus a developer running a 300GB SQL Server database)