The (Version 1.5) was released in April 2015 to address various bugs and enhance the gaming experience. A "decrypted" version typically refers to a file modified for use with emulators like Citra , which requires game data to be in a readable format rather than the encrypted state found on original 3DS hardware. Update 1.5 Key Content & Fixes

There is no performance difference. The "better" version is simply the one that matches the region of your save file. If you have a USA save file, you must use the USA v1.5 update. Attempting to apply the EUR update to a USA game will result in a version mismatch error.