Just find that there are no 15 player and 17 player scenario here is my suggestion.

15 player
scenario name: 3 of each.

3 Sopwith Snipe
3 Sopwith Triplane
vs
3 Albatros D.III
3 Fokker DrI
3 Fokker D. VII

17 player:
scenario name: I am seventeen
2 Sopwith Snipe
2 Spad XIII
2 Nieuport
2 Sopwith Camel
vs
2 Siemens-Schuckert D.IV
2 Pfalz D. XII
2 Fokker D. VII
3 Siemens-Schuckert D.I

P.S. I like unbalanced scenario, btw, what is balanced? Camel vs Camel?

P.P.S. You could also suggest scenario as well.
.