15. A and B start from points A and B respectively at the same time and walk towards each other. A walks 60 meters per minute, and B walks 40 meters per minute. After a period of time, they meet at a point 300 meters away from the midpoint between A and B. If A stops for a while at some point during the journey, they will meet at a point 150 meters away from the midpoint. How long did A stop on the way?
【Analysis】The first meeting time is $(300 \times 2) \div(60-40)=30$ minutes, the total distance covered by A and B is
$$
30 \times(40+60)=3000 \text { meters }
$$

In the second meeting, one person walked $1500+150=1650$ meters, and the other walked $1500-150=1350$ meters. Case one: A walked 1650 meters, B walked 1350 meters, A stopped for $1350 \div 40-1650 \div 60=6.25$ minutes
Case two: A walked 1350 meters, B walked 1650 meters, A stopped for $1650 \div 40-1350 \div 60=18.75$ minutes