hard question- but a great one! I would probably do jumping jacks for 1 minute, sit ups for 1 minute, burpees for one minute, lunges for 1 minute, and push ups for one minute.  I would repeat it 3 times. 

I'd take a walk in my neighborhood.

If i only had 15 minutes I would probably talk myself out of it. I am sooo gooood at that! :-) But if I had to use those 15 minutes moving, I would probably try to run 2 miles. I would fail, and come in about 2 minutes late, but it would be a really hard, fast run and my endorphins would be flying! Also, i would really, really stink. 

Even if II had 15 minutes I'd probably also still have the kids (I really don't get much kid-free time), so the trick would be to make it count with them in tow. To me that sounds like a crazy dance party to loud music- with some jumping jacks and lunges thrown in- or a few races up and down the road. Maybe throwing a frisbee and racing the dog to get it?

It would have to be something I could do with a tot.  Probably walking.  If I could find 15 minutes for myself that would be awesome.

I usually just do really vigorous housework--up and down the stairs, stretches, walking around returning things. I have trouble NOT doing three things at once...