Burn a red steel plate at one point, both sides will burn red, and then open the pressure to pierce it at one time. 15mm is a little thick. If the steel plate burns red, it is easy to anneal, and the steel plate loses its elasticity, that is, it is easy to break. The best way is to use bench drill alloy bit to process holes. After all, I didn't see the product, so I can only answer so much.