Pattern matching

trying to make a .plexmatch file to adjust episodes numbers. Sonarr has different numbering compared to plex/trakt. I am trying to us the pattern function but I'm not getting it to work.

I want episodes 15-27 to show as 14-26. I think this code is correct but I'm not 100% and nothing is happening.

Pattern: Season 3/Season 3{ep,15-27,-1}.mkv