Are there any steps to reduce the size of the folder "URLListLookup" as it is consuming a large amount of disk space?
There are no steps to reduce the size of "URLListLookup" folder if URL reputation feature is in use.
In order to use the URL reputation the client connector must be submitting URL reputation lookups. If SPE is used as a file scanner, and not URL filter for a proxy, the URL reputation feature can be disabled. This is because the lookups would never apply to file scans in that case.
It would be good to understand the feature functionality before you enable and start using it.