According to Patrick the best efficiency for Y Windings Castle motor is 2-4...
A 1512 motor is clearly undersized for a truggy under race conditions, I experienced myself higher runtimes with 1515 than a 1512 in a buggy, so imagine in a truggy...
When the motor is too short, it eats a lot of amps because of its low ratio torque/amps.
5S with increased punch control and gearing for same speed than 4S won't draw more amp than a 4S configuration IMO...