I'd add 15 minutes to your timeline. Set a goal for Boat Dock at 2:45. It might take you longer than expected to get to the dock from inside the park. If you goal is 3pm, and you're delayed, you'd be cutting it close. Maybe I'm just a worrywart. There's no telling what time the boat will arrive at the MK dock. The ride is about 12 minutes, but it's a big boat and takes time to dock, load, and take off again.
EDITED TO ADD: MK has a 3pm parade, "Festival of Fantasy." All the more reason to start out for the dock earlier. The sidewalks will have crowds and paths across roads will start to get roped off.