Here is more info on the Neu 15XX motors:
http://www.castlecreations.com/produ...rs/nm1500.html
BTW...Neil is right...if you run 4S on the 1512 1.5D that comes out to 48,840 RPMs, which most of the folks on here say that it is best to stay under 40,000 RPMS. If you look in the data I printed below...it looks like the 1515 1.5D or 1515 1Y are good choices.
I actually run in the mid to 40K range on one of my road cars and I manage t keep the temps low...but it probably isn't the best for the motor. One thing is for sure...I wouldn't push the motor to spec limits given the cost of those little gems.