15/70 prints are expensive to produce, something like 30-50 thousand dollars for a two to two-and-a-half hour movie. TDKR is the only time a Hollywood film has played at all three theaters in the DC area. It was a big summer movie that was gonna do big business at the box office, so Warner Bros could afford to spend some money on it. There were a hundred or so imax prints made of tdkr.
Interstellar is only getting 50 or so imax prints. It's supposed to be the last Hollywood movie released in actual 15/70, as the digital "replacement" for those projectors is coming next year.
35mm, meanwhile, has all but disappeared. Paramount's final domestic release on 35mm was Anchorman 2 last year. They've said they'll continue 35mm distribution for the overseas territories that haven't caught up yet.
Christopher Nolan and his former cinematographer Wally Pfister are big on not only shooting but also finishing their movies on film. Pfister made his directorial debut recently with Transcendence and there were only 79 35mm prints made of the movie.