My husband & I are sailing on the Wind on 12/25. We always like to get to the port ASAP b/c since we're already paying for the first day we might as well get as much use out of it as possible. Are you arriving by plane on the 15th as well? I would suggest that you get to the port ASAP so you can settle into your room and familiarize yourself with the ship. My 2 cruises before this one, the embarkation process took about 30-45 minutes.
Hope this helps and have a fun and safe trip.