Perform the following on the minute, each minute for 15 minutes:
These will be plenty hard with just body weight thrusters if you don't have any dumbbells. The goal is to finish the "work" during the first 30-35 seconds, resting the last half of the minute. I did this at the gym with 15# DBs and it was really tough. If you choose to use no weight, be sure to "mimic" the movement your hands/arms would make during the thrusters.
We did this last on May 18