NEW YORK (AP) — Christian Siriano marked 15 years in business Friday with Sia performing on his runway and a nostalgic, ballet-inspired fantasy on his models during New York Fashion Week. “I feel really proud of everything we've done,” he told The Associated Press backstage. “All the amazing people we’ve dressed and helped feel confident about themselves.” It wouldn't be a Siriano milestone without longtime muse Coco Rocha sashaying down the runway in something dramatic.