Unfortunately, no, they cannot be re-ordered at the moment. Something to add in the future.
To be honest, I can't remember right now why exactly priority wasn't included in the list, it must have been a very important reason

(perhaps to avoid confusion regarding ordering tickets which are by default ordered by status and priority) Until it is added, you will need to manually remove it from /inc/ticket_list.inc.php if you wish to hide it.