15 turn means the wire is wrapped 15 times around the commutator. Yep, the lower in turns you go, the faster the motor. (Generally speaking)

You could have a high quality handwound 17T that will spank a low quality 15T.

If you are just messing around and not racing then a speed gems 15T Titonite is a great motor. At $30 it's a good price too.