Ordering Posts By Meta Data

First: don’t use query_posts. It will confuse the main WordPress loop.

You will need two queries. First use the query you have already constructed to get the priority posts:

$query1 = new WP_Query( $args ); // here use the $args you already have

Now count how many posts are returned to set the maximum return on the second query:

$count = $query1->post_count;
$args = array ('posts_per_page'=>15-$count) // and any other arguments you may want to parse
$query2 = new WP_Query( $args );

Now loop through both queries to display them. Note that if you need pagination you will have to do some more clever stuff to make sure you get the right posts and amount of posts on your page.