I tested Liferay on two different machines: One vserver with 1GB of RAM and the another with 3 GB of RAM. On the one with 1GB Liferay was very slow. On the second (3GB of RAM) it runs quite good.
My testing environments has just one organization/community and only one user (me). Imagine the situation I would build a portal for approx. 15 organizations and 400 users (30 users per organization) in total. Would a server with 3GB of RAM be enough to run quite fast?
This is very important question for me because of the financial aspect. I don't want to spend 200 Dollars per month for hosting. :-)
Thx.