I did some quick calculations: The energy of the impact from the stored kinetic energy gained by falling fro 15,000m is about the same as half a kiloton of TNT going off. That's focused into a circle just 80cm in diameter.

Yet setting off half a tonne of TNT on the ground, or even just under it, won't penetrate 60 meters deep, or even 15; it will just blast open a shallow crater. A shaped charge will do only a little better.