It's hard to say what might be causing the speed problems in Photo Mechanic without reviewing the log file and possibly the Console entries. To access Photo Mechanic's log file, go to the Help menu, then Reveal Support data. Click the Yes button to open the Photo Mechanic folder in the Finder. The PM.log.zip file will be selected. Attach this to an email to support@camerabits.com. If you quit Photo Mechanic now, you can delete the cache folder inside of the Photo Mechanic folder. Sometimes this is the source of the speed issues in Photo Mechanic. Start Photo Mechanic and try the same workflow. Did this resolve the speed problem?
regards,
--Bob