Depending upon some manufacturers published rpm to define whether or not your tuning is ok is a mistake. To properly tune to the high speed the engine is leaned out to peak then backed off a given RPM margine or as I do is use the pinch method and a brief pinch of the fuel line at full power. If that imediately kills the engine then the main needle is too lean or if the pinch results in a brief increase in RPM then the needle is too rich.

The 15x8 may be a bit to much pitch.

John