Issue: The screen locks after 15 minutes on an iPad in Kiosk mode when set to Never Lock in the Settings>General>Auto-Lock
Detail: You have a corporate profile installed (Email setup through corporate Exchange server)
Solution: Temporarily remove your Exchange email from the device
Additional Information: Outlook now implements password enforcement using Exchange ActiveSync. If your company email policy requires that devices have a password in order to sync mail, Outlook will enforce this at the device level. How this works on iOS and Android devices varies slightly, based on the available controls provided by Apple and Google.
On iOS devices, Outlook will check to make sure a passcode is properly set. In the event a passcode is not set, it will prompt users to set one up in iOS settings. Until the passcode is setup, the user will be unable to access Outlook.
Outlook for iOS only runs on iOS 8.0 or later. These devices are shipped with built-in encryption, which Outlook uses once the passcode is enabled to encrypt all the data Outlook stores locally on the device. Therefore, iOS devices will be encrypted whether the Office 365 or Exchange policy requires this or not.
For complete details see the follow Microsoft Office blog post.