The Eflite BL-15 950KV is rated at 34A continuous and 42A burst

The Motor used in the Apprentice has a lower KV rating so it is LIKELY to be at least 35A continuous capable if not 38A.

Assuming the LOWER rating for safety...

The ESC is rated for 35A continuous. Given that vendors LOVE to make their figure look as good as possible this is likely to be 30Amps AT 11.1v.

So that means the ESC can deal with 35 x 11.1 = 388 watts

If you increase the voltage you must keep the equivalent current draw about the same... sooooo...

388 watts / 14.8 = 26.25 A

You will therefore have to DECREASE the prop size to stay within this wattage range...

Pushing the numbers through ThrustHP...

14.8 x 840kv = 12432 RPM

388watts / 745 = .52 HP

You would need to drop down to a 9x6e prop to draw .54HP which should be within the safety range.

That will produce a static thrust of 2.95lbs but a prop airspeed of 70mph.

The 11x8 prop with the 11.1v pack produces about .67 HP which means that the original electronics were set up to run closer to the "edge", assuming you would use throttle management to keep things cool. The original setup provides 3.82lbs of static thrust and produces a prop speed of 70mph.

If you switched the 14.8v setup to a 10x5 prop you would get 4.49lbs of static thrust but only 58 mph prop speed...

So increasing the pack voltage CORRECTLY will onl net you more THRUST but less SPEED.

IMHO it's not worth doing, particularly on a trainer plane...

A 3D plane would be another matter....