Think PPSSPP is already fast on your PC? Or is it running a little slow in your mobile device?
Just wait until the next release. We are currently focusing hard on performance and have already made some really good improvements, for example FF:CC wasn't really playable on Nexus 4 but on current development builds it's pretty smooth! And GTA runs fullspeed on nVidia Shield with only a frameskip of 1.
Obviously this doesn't mean that a Galaxy Y will suddenly play God of War, but whatever device you have, there will be improvement.
Stay tuned!