This problem has been submitting more for owners of an iPhone 4 and it is a delay when you write on the virtual keyboard.
solution:
Go to Settings> iCloud> Documents & Data here we disable the option. With this all must be solved, so it only remains to test the keyboard and then check if the information and documents we need.
As a final point, if the active iCloud Storage & Backup on, you will have to disable data since the iPhone will enter lag.