It's Probably Known Method in WOD for Leveling which is Pet Battles,but Apparently it still works in Legion and it gives really good exp,i was walking by Lil'idan Wild Pet and i tried to Battle pet some random pet and after battle it gave me 12,450 exp which almost equal to 1 quest, that took like 2 min.
I am not that of a Pet Battler but i saw that this is useful specially if your doing Dailies in your Garrison that's easy leveling.
I hope that was helpful and enjoy