In my experience, that's typically how most CRNA school interviews go. They have a lot of interviewees to get through in a limited amount of time. For every acceptance, there's roughly 3-5 interviewees competing for the spot.
I'd suggest having responses ready for all the standard/common interview questions and a quick elevator pitch of who you are and why they should offer you admission memorized like the back of your hand. Maximize those 15 minutes with clear responses. Of course there will be oddball EI questions, and those are the ones where it's okay to take a few seconds to think. And yeah, it sucks to spend money and time to fly out/get a hotel, only to wait around for hours. A lot of us are in that boat. Just leave it at the door, and be as enthusiastic as you can be. It's 4 hours for your next 3 years/future career. This is part of the test. Show them why you're a candidate they should take a risk on!