If you permanently delete the datasets associated with the job, they will often clear quicker.
That said, if the jobs were actually executing at the time you deleted them, they are already dispatched to the cluster. Your new jobs will start up when there are resources available. Jobs are queued in the order submitted but there is also some management to share resources among all users. If you already have jobs in progress (deleted/purged or not), your wait may be a bit longer since Galaxy has already allocated job slots to you that are not finished.
More details are here: https://galaxyproject.org/main/#user-data-and-job-quotas
Thanks! Jen, Galaxy team