[Soundgod]

If you really hump it, yes, it's 15 minutes.
I was on the boardwalk by Jelly Rolls at 7:23 and was inside the park by 7:42 and I stopped a few times to take pictures.
I was also seated for Fantasmic by 7:54 and was a little right of house center towards the back of the house. I was by myself, so I was able to find plenty of single seats close to show time.
One thing to keep in mind is the humidity and the likelihood that you'll be pretty soggy by the time you arrive at the DHS gate, but you will almost certainly have beaten the boat, even if it were just pulling away from the Swolphin and you're on the Boardwalk side of the bridge. And if there's a decent breeze, your shirt will eventually dry.