How fast was the dyno running at though? The rubber (if there was any) from the roller could easily have an effect on the tire.
It's hard to find a tire in a 15" size these days. I was going to suggest Hankook, as I've had good success with their Venus V4s, V12s, and currently have their R-S3s for autocross.
If you're not doing any digs or anything, just find a decent tire with some speed rating, and when you're going to dyno throw the slicks on.