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.
Your calculations appear to be off by a factor of ~1000. Not half a kiloton, but half a ton (~500kg), assuming fall in a vacuum (upper bound on impact energy):
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MOP_potential_energy = 13607*9.8*15000 # E = m*g*h
MOP_potential_energy
2000229000.0
TNT_specific_energy = 4.184e9/1000 # joule/kg
TNT_specific_energy
4184000.0
MOP_potential_energy/TNT_specific_energy
478.0662045889101
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.
