I'll be dead honest.
I care about staying 1.5 because of ISO's. I don't even use emulators anymore.
The main reason - I need money to buy my DS games, and I don't want to waste it on PSP games unless it's really necessary.
I'm very curious about GTA:LCS, but not enough yet to give up being able to run ISO's off my memory stick. I have the console GTA's and barely played them, got bored fast and hated playing a criminal. So I fear once the cool factor of seeing such a huge game running on PSP wears off, I'll be back to playing my DS again anyway.