C(15,9,2) = 4
Method of Construction: simple construction: multiple of smaller covering
Lower Bound: Schonheim
1 2 3 6 7 8 11 12 13 1 4 5 6 9 10 11 14 15 2 3 4 7 8 9 12 13 14 2 3 5 7 8 10 12 13 15