Only 'fifteen' (of them) showed up on time.
Their boat finished 'fifteenth'.
one 'fifteenth' of the total
(..) Should we get on. It was a simple question. Are we gonna do something or wait here for them to come back around. What time is it? Three fifteen. Over in the rest of the part of the complex should be a telegraph office, Send this to Mycroft, Be back here on the hour. (..)2011 Sherlock Holmes: A Game of Shadows