I'd go along with the 15 flights number.

You didn't specify "successful" solo. My first RC flight 20 years ago was a solo. I sold the pieces, so it was more of a so-long.

From my observations it depends on your attitude, depth-perception, ability to remain calm under stress, quality of your instructions up to that point, and the docility (sp?) of the model you are flying. That and dozens of other variables.

One day while still under tutelage, I arrived at the airfield and was alone. I spent two hours taxiing, eventually getting up the courage to rise off the ground and throttle down to land again. Those two hours did more to boost my confidence than anything else I experienced. Just getting a feel for the aeroplane without the pressure of an audience worked marvels for me. I would certainly recommend a buddy-box, or at least expert instruction. You'll know when the time is right. Our club has a ten week school, and at the end of that time we still had a few students who weren't ready to solo. One of them has the worst depth -perception of any human being I have ever known. I haven't seen him at any of our winter meetings, and that is a shame.

Hopefully your path will be short and fun. It's a wonderful hobby.