I can see where it's possible to change editor fonts, but the project panel font seems unreasonably large. Overriding the default fonts only changes the upper path bar and some other elements.
UPDATE-2016: it is possible, see this
It's not possible, unfortunately, please watch/vote for the bug.
UPDATE: In the later versions global font/size setting under Settings (Preferences) | Appearance also controls the project view tool window font, but there is still no way to control the project view font individually, without changing the font/size of the other UI elements.