[suicideneil]

S = series, the number of cells wired in series.
C = continuous discharge rating, a multiple of the capacity in amps.

Parallel doubles the mah, and keeps the voltage the same, therefore you get double the run time, but also double the weight and size of battery onboard the truck.

If you want to convert a revo, you wont be able to use an MM unless its a rather old one, and even then, its dodgy to run it as 5s when its rated for 3s, or 4s with some mods.

I'd say for best results stick to a 4s 15c 8000mah lipo fomr SPC, or a 4s 20-30c 5000mah lipo from hobbycity; the 1515 1y will be fine on 4s lipo, 5s will be too much for racing (I think many places put a 4s limit on you anyway?).