for regular go-moku (which this is essentially the same) i have never played on a board bigger than 13x13. They use that at IYT...i have played approximately 200 games of that and 2 of them have filled up, both agaginst the same person (lol). 15x15 would certainly be big enough though imo!
(Cacher) Gardez votre boîte au lettres propre en Archivant les messages importants et en utilisant régulièrement l'option Effacer Tous Les Messages. (pauloaguia) (Montrer toutes les astuces)