It's just a matter of the terminology that the manufacturers have chosen to use. A long time ago, standard chargers took 12-16 hours, so when they introduced chargers that took 6-8 hours they called them "fast" chargers. Chargers that take less than 6 hours later got called "quick" chargers. Those chargers that take 15 minutes or something are "super-fast" or "ultra-quick".
The reality is that the fastest you should ever charge a NiMH cell to maintain top performance is 1-2 hours. There are a few chargers around that do that, but not many. What is worse is that if they happen to go wrong, or get given old and worn out cells to charge, they will fry them. How do you like the smell of burning plastic?
Those 15 minute chargers are really not recommended. They charge cells much faster than they are designed to be charged, and therefore shorten their life.
The nice thing about Eneloops is that once they are charged, they stay charged. When you can have previously charged spares to hand, there is really no reason to recharge them at ultra-fast speeds.
