Well here in the USA nitro is cheap and I talked to 2 different brand fuel reps and 15% nitro is their #1 seller. That is fine and Dandy till you recommend 15% to a flyer in a foreign country . Now in some cases you just doubled his fuel cost. I paid $60 for my last gallon of nitro and thought that was robbery since the gallon before was $37.............In the right engines 5% will out perform 15% by hundreds of RPM...........