15. (15 points) Two cars, A and B, are traveling towards each other on a road parallel to a railway. A 180-meter-long train is moving in the same direction as car A at a speed of 60 kilometers/hour. The train takes 5 minutes from the moment it catches up with car A to the moment it meets car B. If the train takes 30 seconds to pass car A completely and 6 seconds to pass car B completely. How many minutes after car B meets the train will it meet car A?