Hi,
Try following Steps:
- Take the database backup
- Stop the database and SEPM service
- Go to: C:\Program Files\Symantec\Symantec Endpoint Protection Manager\data\outbox\ImportPackage
- Delete the files from Import package and monitor it.
Also try new tool:
Shrink the Symantec Endpoint Protection Manager 12.1 embedded database
https://www-secure.symantec.com/connect/downloads/shrink-symantec-endpoint-protection-manager-121-embedded-database