Your calculations appear to be off by a factor of ~1000. Not half a kiloton, but...

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):

  Python 3.10.12 (main, May 27 2025, 17:12:29) [GCC 11.4.0] on linux
  Type "help", "copyright", "credits" or "license()" for more information.
  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