Absolutely. Running Pokemon X without the 1.5 update is like riding a bike with a flat tire. You are risking a save corruption in Lumiose City, you cannot use Pokemon Bank, and you are locked out of custom online servers.
For users on Custom Firmware (CFW) or emulators, the update is typically distributed as a pokemon x update 15 cia top
: For those using older homebrew methods, this update was famous for removing the ability to inject Pokémon created via QR codes. Absolutely
The term "CIA" in this context is unclear. It could stand for several things, but without more information, it's hard to determine its relevance to Pokémon X or an update. you cannot use Pokemon Bank