First, you made a slight miscalculation or mispoke. 15 mls out of 60 mls would not be 15% it would be 25%. Read the reply I made, number 8 down, in this thread to a girl in a very similar situation. You would change the calculation to 3000/15 or a level of 200 ng/ml. If your urine was below this number you should pass if your amounts are correct.

http://boards.cannabis.com/showthread.php?t=77492