I don't know what engines you're comparing but if we take the two OS engines that are those sizes:

The .15 is 6 ounces and is advertised to produce .5hp.
The .25 is about 11 ounces and is advertised at .8hp.

The 25 is almost twice as heavy and produces roughly 40% more horsepower than the 15. Those are significant differences.

Put all the equipment in the airplane aft. Build a stronger area for the battery aft. Don't worry too much that it's weight toward the rear because the airplane will need it. Expect to have a tiger by the tail when you lift it off the first time.

I'd do it. It's an Edge and supposed to be a flyer's airplane. It will be. And it ought to be fun.