9:15AM is not considered a pre-park-opening (PPO) reservation, so you won’t get any special early access or be allowed behind the castle prior to park opening.
For a 9AM park opening, they let all guests in approx 8AM and you are free to roam Main Street / The Hub. Ropes and CMs block further access past the spokes in the Hub.
The welcome show will be at 8:55AM on the castle stage, after which the park opens and you will then be able to walk to BOG for your breakfast.
Hope that helps!