The party starts at 7.
By 7:15 Ohana will most likely be behind. I would not expect to be seated at 7:15, but rather 7:30 or later. Even if you were seated at 7:15, plan dinner to take at LEAST an hour (8:15) and then you have to get back to MK. This would put you at entering for the party at 8:30-8:45 depending on your luck with transportation.
I would get a different meal. That is wasting WAY too much time of the party.