You will need 15 weeks to play all the other teams twice. For example:
(A B) (D F)
(C E) (A D)
(B D) (A F)
(D E) (C F)
(A C) (B E)
(E F) (C D)
(B F) (A E)
(D E) (B C)
(A E) (C F)
(B F) (A D)
(B C) (E F)
(C D) (A B)
(D F) (C E)
(A C) (B D)
(A F) (B E)