Three seconds to update after a button press? Sum Ting Wong. Big time. On my MEGA's, with 21 modules connected, when I enter a new "message" via Bluetooth (9600 baud), 400ms later I have a new message scrolling in the display.
I'd be looking at what exactly you're doing AFTER the button press since that's where the slow down is. Plus it really shouldn't be variable delay either so I'd be looking at whatever the "state machine" is doing and why it's taking so long to do it.
You want to do a quick test, skip the state machine calc's and just display a message after the button press. That'll narrow it down I would think.
Mel