Plyometrics refer to any move where both of your feet leave the ground at the same time. While these intense exercises aren't for everyone (skip them if you have knee, hip, back, or other injuries), they amp up the intensity of your workout like nothing else can. You'll be soaked in sweat long before your 15 minutes are up!
Do each exercise for 1 minute, moving from one to the next without rest in between. After you finish the last move, rest for 1 minute and repeat the circuit 2 more times, 3 times total.