One dead crook is a good thing, but
"and probably had just seen his life flash before him"
with the time it took to fire 15 rounds it was a pretty long "flash"- just how OLD was this pizza guy anyway ?
Pizza guy - 38.
Dead thug - 20.
Try it sometime. You can empty even a revolver with a long heavy trigger real fast. If it is a semiauto with a light, short trigger, the perp won't even have time to hit the ground.
That said, most people who find themselves in this situation stand there pulling the trigger on an empty gun for several seconds before they realize it is all over. The adrenaline shock messes up your perception of time.