I am not sure if this has been reported before, but this is a new bug I have come across.
I found this bug when I was editing using the Edit function from the "Button Setup" but have confirmed that is also present in the Edit function in the "Select.." interface for Script Triggers
If you happen to Edit a Script in the following manner from Layout Mode, double-click on a button
Click on the name of the script to go in to the editing interface.
Select a line in the script and use the Cut Function (Command + X)
FileMaker 15 will crash.
So far this crash has occurred every time I have tried to use the Cut function in this particular script editing environment. It does not crash for Copy or Paste.
It should also be noted that the crash does not occur from the Manage Scripts (Command + Shift + S) interface.