If you install Ubuntu 15.04 and find yourself running out of memory, login as root, fire up bum (Boot Up Manager) and untick all the garbage you aren’t going to use.  There is just way too much junk installed and enabled by default.

     On my workstation machine, I got the RAM used when logged in with my normal array of half a dozen terminals and Firefox down from 3GB to about 700MB.  It also made start-up and login a lot faster.