That weight on that size engine will definitely have some "flywheel effect" both on acceleration and decceleration. You'll find it will take a tiny bit longer to wind up from lower rpms, and when you back out of full throttle the rpms won't immediately drop as they do without the weight. It's true, it won't be as profound a difference as it would if the weight was further out from the hub, but you're not talking a lot of torque with a .15 engine. I think you'll notice a difference, but is it enough to hurt performance? You'll have to try it to see. It's not like it's a permanent thing, if it hurts performance, take it off and go to plan B for balancing the plane.