iOS 9 Removing Camera Access From Lock Screen
It's looking like you cannot suppress the photo icon from the lock screen and iOS 9 has no difference in behavior from iOS 8 (so this really looks like a duplicate question to me since iOS 5 in fact...) unless you disable the camera entirely - lock screen or not using a MDM profile or restriction in the settings app.


Removing camera button on iPhone lock screen


The only countermeasure to that malicious behavior would be to not let the camera participate in iCloud photo stream so that once the camera had filled up the storage on the phone, the phone storage would be filled.

Bulk deleting images is something that's easy with a Mac and the Image Capture app.

In my opinion, this is a bug, and Apple should allow a restriction to prevent use of the camera from the lock screen. You could cut off the camera entirely using restrictions or an MDM profile, but that would prevent all use of the camera and not just from the locked state.

I would reach out to iCloud support and explain the data loss - they can point you to the upload restrictions and possibly tune them using your actual bad experience with Photo Stream.