I'm currently using a VPS with this configuration:
16+ CPUs Equal Share
2.5 GB RAM
RAID-10 HDD (not SSD)
CentOS 64bit + Apache + CPanel
But the back-end performance is extremely slow and frustrating (the front-end is slow, but useable).
The hosting statistics shows that very rarely We're using above 2.5GB of ram, the average is 1.7GB.
What do you think causing that?
Also, to this system do you think it make sense to move to a 4GB setup, or 2GB with LiteSpeed should work better? (I don't know if LiteSpeed can lower the memory usage and provide better performance, It's a total noob question).
Why not go with more RAM and still use LiteSpeed (preferably with LiteMage Cache as well)?
You can allocate the extra RAM to MySQL for MySQL Query Cache and InnoDB Buffer Pool.
Also, while you are at it, consider switching from the slow HDD to SSD as well.