That issue has plagued each and every Disney cartoon-to-stage adaptation and I've never been sure why. Disney cartoon films tend to run about 90 minutes, give or take a few. But the stage musicals almost always clock in at close to 3 hours. Now the obvious problem is that the young kids, who are a large part of the target audience, just can't sit still or stay awake that long, but the other issue I've found is that the new material written to extend the length of the show is almost never up to the same quality as the original film material. So not only has the show been bloated to double the length, the new material isn't as compelling and doesn't make the case for it's necessity.
Every Disney show I've ever been to on Broadway has seen the kids fast asleep after intermission. And the adults shifting in their seats and waiting for the finale so they can go home. ThE LION KING was especially egregious because there are long stretches where the actual story is forgotten in favor of yet more stagecraft.
I've never understood why they shows can't be, as you state, an hour first act, fifteen minute intermission, and 45 minute second act. A 2 hour show would accommodate an intermission to sell crap to the kids and would only necessitate a small bit of extra material added, some of which you'd probably need anyway to facilitate the adaptation.