If you want the maximum wait time to be less than 15 seconds, say ~15 seconds, then set the Destination if no answer time to 15 seconds, have it connect to your next hunt group thereafter.
Remember that if you set the DNA to 15 seconds as shown above, and you've set the queue to Prioritized Hunt, with a Ring Time of 15 seconds, only 1 extension will receive the call. It's best to change the Polling Strategy to Ring All.