No clue. The Guidance is rather vague. And it's a great question.
I immediately think of both Rise Before Dawn and Target Run in Star Wars Land. Those have you indoors for over 15 minutes as the "attraction". Also Haunted Mansion, Star Tours, Mission:Breakout, Indiana Jones, etc.
But then the actual time you are sitting in a moving vehicle on all those rides is only between 5 and 10 minutes. But does the pre-show and indoor loading process count towards that 15 minute limit? Because most of those rides would go beyond the 15 minute mark even if they are total walk-ons in a nearly empty park.
Then there's the Submarines. They slowed that ride down for the Nemo version and now that ride takes about 12 or 13 minutes. But you sit in the Sub for much longer than 15 minutes for the loading/docking/mooring/unloading process. Submarine Voyage would seem to be forbidden just because of those logistics.
The only other rides I can think of where you sit in the same vehicle for 15 minutes or longer is Pirates, Small World, and the Disneyland Railroad. But the Railroad is mostly outdoors (except for Grand Canyon Diorama and Primeval World for 3 or 4 minutes) and It's A Small World is indoors for about 12 minutes, while your boat floats through the outdoor gardens for several more minutes.
Why didn't Walt invest more in Tilt-A-Whirls and less in epic E Tickets?!