The 15 minutes after block in is to allow for post-flight duties. It also has nothing to do with FDP, so has no bearing on legality.
Originally Posted by
Cloud5urfer
Fair point. Unfortunately, to my knowledge the company can change the FOM to their liking regardless of CBA. Only thing we can argue is if the post flight duties take longer than 15 minutes, be sure to make crew services change your duty off times for legality.