Hi Hans, Welcome to the Staboard Forums!
For 10-15 knots, if you have some experience sailing the hire kit, you would want at least a 7.5 m2 rig on the Carve 133.
How much you weigh can have a significant impact on yoiur sail size, as well as the fct you are sailing on fresh water.
A 6.0 would do as a trainer sail, but you will never get planing in 10-14 knots.
If (as Agrelon suggests) you get 15-20 knots, then the 6.0 begins to make much more sense.
Hope this helps,