Is 16GB of RAM enough for running multiple VMs simultaneously?

No, 16GB is not enough for multiple VMs running at once. Each VM needs 2–4GB just to boot, plus the host OS, leaving almost no headroom. Once RAM fills up, swapping slows everything to a crawl and can crash VMs. For a test lab or dev environment, 32GB is the realistic minimum; 64GB if you’re running Windows Server or heavy Linux desktops.