In the most cases its not a bad change. only the feathers. In 12 kg we already build monsters. With 3 kg Extra I myself am capable to put heavyweight sized FP setups in feathers.

or else, build steel armoured bricks. if you know there are already full hardox armoured feathers -BonX for example, with a 2 Kw drive.

No, 12 kg is a challenge to build a feather, 13.6 kg is already nuts, but 15 kg.... Imagine a Scorpion junior using a Perm 080 for weaponmotor. Nor fun nor cheap to compete in the 15 kg class.