I created a FMP15 file and tried to open it with FMP14 app. File extension is .fmp12.
Received this message:
This is version 14.0. “Video Contents Copy.fmp12” was created by version 15.0 of FileMaker and cannot be opened by this version. Please use version 15.0 to view this file.
Since it's using .fmp12 extension, I would assume it would open the file.
If this the case, then it is going to be a very SLOW conversion to FMP15.