SQL Server seems to slow with batch deleting the spam, we believe because of the transactions. We’re looking into speeding it up, but one way to work around it for now is to do some of the deleting outside the HelpSpot interface. The link below has a script for deleting spam which directly deletes spam. It won’t train the system though, so you can use this to delete most of the spam, but you should still occasionally manually delete it so that the system can learn from the spam.
It sounds like your system is well trained so it should be safe to do this as long as you occasionally do it manually so that the system can learn new forms of spam.