Yes, but less than you think. The two decrypted updates are functionally identical in terms of code. However:

By securing the Pokémon Y Update 1.5 for your decrypted 3DS collection, you ensure that your trip through Kalos is free of the technical hiccups that plagued earlier versions.

: Resolves a rare issue where the game could freeze or save data could become corrupted when saving in Lumiose City. Internet Connectivity : Required for all online features, including the Player Search System (PSS) , Wonder Trade, and the Global Trade Station (GTS). Performance Improvements

If you’re replaying Y on an emulator or a CFW console, track down the decrypted 1.5 update. Your Lumiose City saves will thank you.

If you are downloading a file labeled "Decrypted," it means the ROM has been modified to be played on non-official hardware or software.