(If there's not one nearby, you could always start one... when I cofounded a hackerspace I met a lot more than 15 new people who wanted to share 3d printers and the like!)
I'm going to guess your situation is a lot more common than RaphiePS'. I know quite a lot more than 15 people, but not 15 who live in close enough proximity to make this work and who are also likely to be interested in co-oping on a 3D printer.
In any case, 15 sounds like a bit of a logistical nightmare even if you did have that many people in your local friends circle interested enough to go in for a 3D printer.
I'm in high school, so it was pretty easy to find some interested friends. It also helps with the logistics--we keep the printer in the computer lab so everyone can access it.
