I have not heard the 15knots thing before?? some of my lesons were in winds stronger than that!
As for the 25 hours i am an experienced model pilot and picked it up realy quick. I passed my Skills test before 25 hours then had to do further flights to reach 25 hours.
it also helped that i bought a new C42 to learn on and my instructor devoted himself to me every day and it only took a few weeks from start to finish.
there are guys at our strip that are up into the 50-60 hours in a CTSW (with the same instructor) and not passed yet and another that also did it in 25 hours (CTSW)
Dave