Go for lipo power + the Traxxas 12T brushed motor, since the Arrma 15T will not survive for long.
Since I guess you have a 2014 or later model, I would not recommend serious brushless power. There are no metal upgrade gears available, as a metal differential.
You could try a modest brushless set like a 2-pole 2700-3000kV 540 motor. That will be much faster than the stock motor, will give longer runtimes as a bonus and is not that harsh on your composite gear box and differential!
That said, the 2013 BLX Granite has been basher or the year. On 3600kV BLX power it was a high fun idiot power machine on 2S lipo, on 3S mind blowing!
Thanks to the metal gears it could handle the power with ease.