This worked for me in IntelliJ 14.0.3 Community Edition in Ubuntu:
File | Settings | Appearance & Behavior | Appearance
And then tick on:
[ ] Override default fonts by (not recommended)
Name: Ubuntu Size: 14
There you can choose the font and the size of everything: menus, Project panel, Editor, etc…
For me, on Linux, it is fine to set it to 15 (default is 14), and then adjust the Editor font alone under:
Editor | General
Mouse
[ ] Change font size (Zoom) with Ctrl+Mouse Wheel