We got one very rainy day last month. Crowds were so low we practically walked onto everything, right up to every character, so on.
We were lucky enough to be at one of the really close hotels, and to have the rain be on our world of color day. We were pretty miserable around 1pm (when the rain was the worst) so we grabbed our picnics and took them back to our room. We sat and ate while our pants and shoes dried, and we changed socks and grabbed different hoodies.
As long as you have some sort of rain gear, I think you'll be fine. We had a lot of fun day, all except the hour before we took our break, but it was our fault. We had no rain protection at all, so we were drenched to the bone and cold, not to mention a little grumpy. Had we prepared even a little, I doubt we even would have needed to take the break at all.
It'll be fine, and like others have said, 15 days out the forecast means NOTHING. The forecast for our days literally changed every day the whole week leading up to leaving, and not just by a little. It would go from a 40% chance of heave rain and 40 degrees, to 70 and sunny, and everything in between. It even kept changing WHILE we there. We were supposed to have 3 rainy days, and only really had the one.