The pathfinder behaviour uses a simple grid-based A* search algorithm in order to determine routes between cells. Assuming you're using the default cell-size of 20, then your algorithm is generating and searching through 13000/20 * 6000/20 = 195000 cells.
So, yes, I'd say it's normal to expect that to slow your code down ;) Either reduce your layout size, increase the cellsize, or build an alternative routing algorithm that uses a more sparse graph.