It depends what you want to delete. delete_from salesTable deletes sales headers and related sales lines and stuff related to lines and so on. Also it is triggering standard delete validation that prevents you from deleting this order because you should process output order first.
If you don't care about all related data and want to delete sales order header and lines you do this from SQL, it would be even faster, however, it could cause data inconsistency and corruption, so don't do this in prod.