I don't think there's a way of knowing which campus's roster is filling up quicker, although generally the Colorado campus is more competitive than the Utah campus. When you apply through AACOMAS, there is one application for Colorado/Utah (where you select a preferred campus, and then select if you're willing to interview at your secondary campus if you don't get in at the preferred one), and a separate application for the Montana Campus. So I think if you're trying to maximize your odds, you'd want submit both applications, and then on the Colorado/Utah application you'd want to put Utah as your primary. Although, I don't know if being an international applicant changes that picture.
For my interview at the CO campus, it was a 30 minute conversation with 2 faculty members (they sent the Zoom link and names of faculty a few weeks before the interview), mostly unstructured. They asked me a few questions at the beginning, then there was free time for conversation and my questions. The interview was closed-file, they only have your essays and letters of recommendation.
As for the post-interview acceptance rate, yeah I think that's pretty unusual, but I wouldn't worry about it. I work as a medical assistant at a neurology clinic in Colorado, and all the docs I talked to said that RVUCOM is a great program, and I know a few classmates from grad school and former MA's at the clinic who've gone there have loved it.