I did a speech about FIRST for my public speaking class. I can tell you that it is very difficult to squeeze FIRST into that length of time, and I didn't talk about the other branches of FIRST either (FLL, FVC).
I'd say stick to FRC. Talk about the history of FRC, all the benefits it has (students, mentors, businesses) and your experiences with it.
I also have a 1 minute clip from the beginning of the promo video FIRST made.
http://download.yousendit.com/B374B1B35733E8BC