Depends what’s holding that space now. If you delete tickets that doesn’t mean it immediately deleted associated attachments which is where the bulk of the storage is. They get queued for deletion and should be removed after 24 hours (assuming you have a Cron job).
You will need to check what’s holding the storage as in actual data or just MySQL itself is holding on to that space. Its likely you don’t have MySQL's innodb_file_per_table setting enabled so it’s not automatically reclaiming storage on data deletion. There are many guides online that explain how to reclaim storage in MySQL.