Hoping for some advice in which direction to go here.

I have a need to set up desktops for two users to access a postgres server from over the interwebz.

My thoughts so far are:
Install Postgres on one server (done)
Install KVM on another server (done).
Install Ubuntu desktops on KVM server (done).

The issue I find now is that the Ubuntu desktops are too slow (probably due to using an old test machine)

The environment will expand over time to maybe 20-30 users (within a year if we're lucky), I don't think my current method will be scalable.

Pointers please;
am I going about this the right way?
is there software better suited to this environment?
are there quick ways to deploy desktops?
are there configuration options I should look at for the guest OSes?