Yup. In my experience a stable server requires about 700MB of RAM. There are reports on https://www.reddit.com/r/admincraft/ saying you can run it in 200 MB but I haven't managed. Probably with the right swappiness settings, performance tuning of the JVM and the Spigot / PaperMC instance.
So 16GB of ram should be enough for 20-60 servers.
So 16GB of ram should be enough for 20-60 servers.