Hello Eugene, that process is slow as you mention, when deleting it has to go into several tables and delete all relations between objects before deleting objects. If you are deleting all tickets and everything in the system then the best way is to drop database and create it again, otherwise best thing is wait, depending on the configuration of your machine that might take you about 10-15 hours,
Best thing to do is configure generic agent to run every 10 o 20 minutes. It deletes about 4000 tickets each round.
Regards.