[suicideneil]

Amps vs voltage concept:

power (watts) = volts x amps.

You need a certain amount of power to move any given setup to a certain speed.

If you use a low voltage, high current (amps) setup, it will run hotter and give less runtime compared to a higher voltage, lower current setup.

For example:

1000watts / 14.8v (4s lipo) = 67amps
1000watts / 11.1v (3s lipo) = 90amps

The more current you pull, the hotter the system will run, and the shorter the runtime will be, all things being equal aaprt form voltage.

That said, your 1515 1.5D would run equally well on 3s or 4s, you just have to match the gearing to the voltage to keep temps, speed and power in check.

I would peronally run 4s lipo, and gear down a bit to reduce the load on the electronics, yielding the best runtime, acceleration and power available.