Amp draw/efficiency question

[nuz69]

This thread illustrate the "sweet spot" issue of a brushless motor.
Low Kv and low voltage isn't good, high Kv and high voltage isn't good either. You are comparing Low Kv at low voltage and mid Kv and at voltage. The low Kv motor has smaller thickness of its widings wires, that's why it does'nt like high amp draw and need more voltage at same power, but that's why low Kv keep the ESC cool and happy.
==> I would say that geared for the same speed and at the same voltage, the higher Kv would be best.
It's also for thoses reason that we speak about "sweet spot" for brushless motor and why a certain minimum and maximum RPM is advised. For the 15 neu series, the "sweet spot" (according to most users) would be between 35 and 40K, so IMO the 1,5D would be better and run cooler at the same power.
NuZ