You shouldn't need more than a layer of 2 oz. and a layer of 6 oz. on the F-15 nose. Additional layers only add weight. You can lay a piece of 2" tape longitudinally on each side for a distance if you want a bit more rigidity. If you have issues with flex, it may be the resin you're using. When using epoxy if the mix ratio is not correct, you can create a situation in which it never fully cures and stays a bit "rubber ducky". Sometimes it's just the brand of resin you use also.

Larry