EPIM speed depends on your USB stick speed mostly. Try to empty Trash and delete old unnecessary items. You can archive old records with our free tool EPIM Archiver/DupRemover. The latest version is available from our download page - http://essentialpim.com/get-epim
You can also try to Optimize database (File -> Database management -> Optimize).
Try also to reformat USB drive.
These measures should boost performance.