I have put a range of schedules below. I think you have realised that even numbers of teams are better, since you can have everyone do each event exactly once, so I have put these schedules first. For odd numbers of teams, there will always be one team per event who plays twice. Where this occurs I have highlighted the team that plays twice in the last row.
12 teams (A to L) 6 rounds
(F L) (J A) (I E) (H K) (G D)
(H J) (I F) (C K) (B D) (A L)
(C G) (K D) (J L) (A E) (H B)
(B K) (L E) (H D) (G F) (I C)
(D E) (C B) (G A) (I L) (J F)
(I A) (H G) (F B) (J C) (K E)
14 teams (A to N) 7 rounds
(I A) (F N) (B G) (C M) (J E)
(N B) (K L) (M E) (D A) (I H)
(H G) (C E) (I L) (J B) (F M)
(J L) (H D) (N A) (I K) (G C)
(F C) (G M) (J K) (L E) (B D)
(K E) (I B) (F D) (H N) (A L)
(D M) (J A) (H C) (F G) (N K)
11 teams (A to K) 6 rounds
(D K) (F G) (E C) (H B) (A I)
(G A) (D C) (F I) (J K) (E B)
(J B) (F H) (E K) (C A) (G D)
(E H) (A K) (J D) (G I) (F C)
(F A) (B I) (G H) (E D) (J C)
(C I) (E J) (B A) (F D) (H K)
A F E D C
13 teams (A to M) 7 rounds
(I B) (A C) (L K) (F D) (M E)
(M C) (J I) (B E) (H G) (A D)
(E G) (K D) (C I) (A L) (J F)
(H K) (M G) (F A) (J B) (L E)
(I D) (J L) (M H) (C E) (K B)
(J A) (F B) (L G) (M K) (H I)
(F L) (H E) (J D) (M I) (C G)
I J L M E
15 teams (A to O) 8 rounds
(D J) (L E) (A F) (N O) (C B)
(A K) (J L) (B N) (H G) (M I)
(C O) (B F) (M K) (D E) (A L)
(J F) (G I) (D H) (K L) (N E)
(M L) (H O) (C J) (A B) (D G)
(N G) (D C) (E O) (J I) (K F)
(B I) (A M) (L G) (C E) (H J)
(H E) (K N) (A I) (M F) (D O)
J L A E D
