Just to be sure that cpu is working at max frequency try installing "Cool Tool" from the market, it will show an osd that tells you the current cpu freq.
Then try playing with ppsspp and see if it's always at 1,5ghz, see also if cpu is at 100% usage.
Then try playing with ppsspp and see if it's always at 1,5ghz, see also if cpu is at 100% usage.