Q: It will run from 10-15 minutes. I'm thinking that I should cover the basics first and then if there's enough time, I can show them one topic like how to make a 3D graph. I don't know what's the best idea.
A: Depends on what the audience knows. If they're total noobs, I'd cover just the basics of vector art, using the selection/pen and transform tools. Any extra time I would use to show various examples of vector art and if you don't have any in mind Illustrator comes with some pretty impressive samples. If they're too advanced for that I'd try some of the newer features, Live Trace, Live Paint and then if there's time explore the 3D effects.