Four people want to cross a bridge at night with just one torch (the torch is needed to cross)

Four people want to cross a bridge at night with just one torch (the torch is needed to cross). Crossing takes them 1, 2, 5, and 10 minutes respectively; crossing together means going at the slower person's pace. Rohan thinks always taking the fastest person (1 minute) along as an escort is the best method, taking 19 minutes total. His sister says there is a better way — in 17 minutes. Who is right?