Linux always takes all the memory. What is not directly needed is used for cashing.
Better have a look at the VM. For example, with htop or webmin.
That’s enough for full installation (Collabora Online, RocketChat, Guacamole, …), many open documents under Collabora Online and a lot of users.
But if you have that available…
You should, however, add a processor. At least two.
EGroupware will certainly run more smoothly.