C(15,6,2) <=10

Method of construction: lex covering

 1  2  3  4  5  6
 1  7  8  9 10 11
 2  7 12 13 14 15
 3  4  8  9 12 13
 3  4 10 11 14 15
 5  6  8  9 14 15
 5  6 10 11 12 13
 1  2  8  9 10 11
 1  2 12 13 14 15
 1  3  4  5  6  7