16GB will handle three 2GB VMs.

Yes. With 8GB, two VMs (4GB total) already strain the host—Windows or Linux needs at least 2GB to breathe, so that third VM pushes you into swap. 16GB gives you 6GB for the VMs, 2-4GB for the host (depending on your OS), and still a few GB of headroom.

That headroom matters because VirtualBox itself uses extra RAM for page tables, video memory, and caching. So 16GB isn’t overkill; it’s the minimum for three VMs doing real work.

Just don’t forget CPU cores and disk speed. If you’re only adding RAM without enough cores or an SSD, you’ll trade swapping for CPU thrashing. But the question was RAM—and 16GB ends the swap problem.