RSNovi,
It doesn't mean anything by itself. The highest priority a dealer can use is a 10. That said, he may never use that. He might start at 15 or 20 so that he leaves himself room underneath existing Retail or Stock orders if he gets something he really needs to move on.
Orders with different priorities between dealers don't compete with each other, so if your guy uses 19 and another uses 10, it won't matter.
What you really need to know is how many vehicles he is allocated by Ford, how many orders of the same or lower priority he has to fill, and if he can get Retail orders filled outside of stock allocation. If he's forthright, he'll tell you where you are. But he's not obligated to do that. A salesman can't usually tell you - you need an ordering manager.