You can't play GTA on 1.5 since GTA was encrypted using the keys from 2.0.
Full emulation of 2.0 firmware on 1.5 has not been implemented, so even that method won't work.
ISO loaders REQUIRE kernel-mode access in order to bypass UMD checks so they won't run on 2.0 since kernel-mode exploits for 2.0 have not been found yet.
And even if the exploits are found, the loaders themselves will have to be updated to support the newly found exploit.
But it's fun watching the script-kiddies on other forums try to run it via some of the loaders, swapping files between different games, thinking it's going to work.
I don't have the heart to tell them that it's never going to work that way, they just seem so determined to keep driving down that blind-alley, running into walls.