This tutorial explains several methods of how to split a clip in iMovie 10.1 (Late 2015).
iMovie 10.1 – How to Add Music: https://www.youtube.com/watch?v=aA84k799NS8
iMovie 10 – How to Fade an Audio Track In or Out: https://www.youtube.com/watch?v=uwBRn35xJ4Q
This beginner tutorial covers splitting a clip by right clicking it, using a menu option in the modify menu and by using a keyboard shortcut. iMovie 10.1 is also known as iMovie 2015.