I have 1515 rail buttons on my Wildman Extreme, which weighs about 26 pounds with a four grain m motor. The reasoning was that the larger/longer pads where I fly are 1515. You could easily fly this with 1010 though.
Most launches will have 1515 rail pads, but they will usually be further out.
What really matters is thrust to weight on takeoff. Ive only ripped off one button. It was launching a PML Explorer on an H999. The pad tipped over too. [emoji16]