At 15:00, its a stall turn at the top of a vertical climb. Basically, you go straight up, bleeding all your airspeed and energy, and right before you lose all forward momentum, kick the rudder hard one way. The plane will rotate it's nose back down with almost no forward(upward) movement. It's like hanging in space for a split second, then coming back down full bore.
Scary move to use in a fight, as you are motionless, energy-less and a very easy target if someone has you in their sights. But... if done right (like in the video), you have someone behind you trying to get you, and they run out of speed/energy first, it's a great way to quickly turn the tables on the would-be attacker.