MMM 6s vs. 4s

[jnev]

The super high RPM's are what cause the motor to heat up in this case, and especially with low gearing like that, you'll cause the motor to over-rev causing even hotter temps. I wouldn't go higher than 5s on the 1515/1y, and 4s on it is ideal in my opinion. On 6s, anything with the KV going from the 1515/3d to the 1515/2.5d would work great.