The "decrypted" version means the update has been stripped of Nintendo’s 3DS signature encryption, allowing it to be:
Fixes errors that occurred during Global Trade Station (GTS) transactions. pokemon x update 15 decrypted 3ds eur usa upd
pokemon_x_update_15_decrypted_3ds_eur_usa_upd.rar The "decrypted" version means the update has been
UPDATING SAVE FILES... APPLYING PATCH 1.5... SYNCHRONIZING REGION DATA: USA/EUR... pokemon x update 15 decrypted 3ds eur usa upd
Fixed animation errors for various balls (Great Ball, Ultra Ball, etc.) when sending out Pokémon. Why You Need a "Decrypted" Update File