What is 1.5? I mean game wise, just HD Version of 1?
It's a PS3 remake of Kingdom Hearts 1 and Kingdom Hearts Re: Chain of Memories (which is itself a remake of the GBA Chain of Memories game) and the cinematics from 356/2 Days from the DS with added voice acting.
I considered picking it up, but tbh... I own Kingdom Hearts 1, I own Re: Chain of Memories (the original too), and I hated 356/2 Days.