I don't have a 15-22, but I do have a GSG-5 and the Blazer .22 worked so well in it I picked up a case of the stuff at the sporting goods store when it was $16 a brick of 500.
I haven't tried it but I wouldn't hesitate to use it, My 15-22 Loves the $1.47 a box Federal from Wal-Mart so thats pretty much all I have been shooting in it.