PPSSPP 1.15

[LunaMoo]

That's just your device throttling when you aren't using touch controls. Most phones aren't made to sustain higher cpu clocks and the only apps that can utilize more power of a smartphone are popular apps and benchmarks which they whitelist to make their device look better for marketing purposes.

Unless your operating system has an built-in option to do something about throttling when touchscreen isn't used, you're out of luck since it's not a problem that can be fixed on PPSSPP side.

At most you could try messing around performance options hoping something changes your OS mind about conserving power when PPSSPP is running, use auto-frameskip hoping it's enough to at least keep the speed at 100% when your phone throttles or just stick to lighter games that can run well even when your phone is at it's potato mode.