RE: slow stick flight time
The C-12 on the ESC is a part number. It is a 12 amp ESC nothing more nothing less.
The 15C on the battery is another story. 15C means it can deliver 15Xthe Capacity of the battery continuosly. A 1500mah battery with a 15C rating would be 1500mah x15= 22500ma or 22.5 amps. That does not mean the motor will draw that much it just means that the battery, if pushed, can provide that much.