Q: Task Manager slowing down

You could try restarting both iPhones and then make sure you are bringing up the recently used apps list from the home screen.

If that doesn't work and you beleve one of the iPhones is slower than it should be, you could always try restoring it.

This is happening because your device is set to have a triple click function (such as VoiceOver, inverting colors, etc').

In order to remove the 'delay' you must disable the triple click. You can do it by going to settings -> general settings -> accessibility -> triple click(at the very bottom) -> off.

Hope this helps