I just learned a small trick from the interwebz. It speeds up iOS by cleaning up RAM and processes:
- Lock your iPhone or iPad.
- Hold the power button until you are told to slide to power off.
- Press and hold down the Home-button for 5 seconds.
- That’s it!
I tried it and it seems to do the trick. Supposedly this has been possible to do for ages, but I have only done this on iOS 9.x.