If the bed heater is wired for 24V then it's most unlikely that it will draw more than 15A. Are there any more pads or wiring legends on the back of the board, apart from the "12V" one in your photo? What's underneath the blue tape?
EDIT: maybe it's really a 12V-only bed, and the 12V/24V connection instructions on the front are left over from when the original design was cloned? The instructions on the front suggest that there should be 5 pads, but in the photo I see only 4.
