Hi Raul,
Jerzy told me the reason for Sebastian Kawa not to compete with the GP15 prototype were problems with its wing surface (reducing the performance). Next wings will be better.
I was visiting the company last weekend and a friend did a testflight. He was very impressed - strong engine, nice to handle, very quietly while gliding. But he felt not so good while circling with high banking. There were a few other minor problems (radio antenna, error in the engine computer, difficult assembly of wings) - i am sure these points will be cleared soon.
My guess is the biggest problem for gp is finding and training a big number of good workers.
L.