Hello aspirant

As, your friend got 15th rank in JEE Main, so he has prepared well for JEE Mains. Getting 100 percentile requires hardwork and smartwork. It also requires ton of practices to attempt all questions and correct all questions. From the score card of your friend he is well prepared, so if he performs same in the JEE Advanced exam, so he will surely get top IIT colleges. But, the only criteria is that he performs well in JEE Advanced too, because getting top ranks in JEE Main doesn't ensure you top IIT colleges.

Hope this helps.