Very good tips!!!

First is my favorite, but you don't even need 15 minutes, you just have to fall asleep.

I have a trick:
I would take keys in my hand and relaxed so when I fall asleep I will drop keys and immediately woke up. That's it!!! You are fresh in few seconds.

I could do that 2-3times a day (every 3-4hours when i feel sleepy) and work for 16 hours or more. Sometimes work was driving, but in that case, don't push it.