First to Threshold:
They have not reached Warp 10, this was just a rounding error. Paris' visions of planets were hallucinations, there were caused, along with that devolution by a energy field generated by the new form of dilithium.
That Warp 10 puts you everywhere is a myth. It is not supported by any hard facts.
Just think, they went "Warp 10" twice, so the probability that the shuttle would show up near its starting point are abysmally low.
To Warp 13, or Warp 15:
It can just mean that 0-10 is the standard TNG warp scale and >10 are transwarp/quantum slipstream velocities.
Warp 11 is Transwarp 1, Warp 12 is Transwarp 2...