I am responsible for looking over a couple hundred iPads, and we use Jamf to manage them. I have a good amount of inventory at 15.4 that hasn't been enrolled yet.
When 16 is released will Jamf auto-update them to 16 during enrollment? This would be incredibly bad for our environment.
Jamf Now specifically won't push out OS Updates automatically. iOS has built in mechanisms that prompt users to update the iOS. But Jamf Now specifically shouldn't be the originator of the OS Update (unless you intentionally push the update via the OS Update workflow shared below):
You can also use the "Delay OS Update" feature to make OS Updates not available for the specified time:
TL;DR - Jamf Now won't automatically push OS Updates to devices without your consent.