I understand your concern as well. I agree with Cruise Fanatic about going down a day early. Cruise Fanatic also makes the point about the ground transportation being included. They will be aware of any delays. They will not cut off embarkation strictly at 3PM if there are guests on the way from the airport.
You could be as late as 2:30PM without any issue at all with the ground transportation.
Just in case though, I want to give you the Travel Hotline Number 1-877-855-4856