I'm assuming you're talking about the US? You want Rule 4051, which says that adult events may not exceed the maximum time allowed, but may be less provided the technical elements are included. For free skates Preliminary and higher, programs must be within 10 seconds +/- of the required time. Most people try to be pretty close to the maximum available time, though, because they can fit more into the program that way. You could try either cutting another piece of music together with the one you like, or look for a section of the music that could be repeated. It is also sometimes possible to slow the music down slightly and stretch it that way. That likely wouldn't work for your example, though - if you stretched the music another 15 seconds longer it would probably be too slow to sound good.