Honestly La Nostica (Limsa area) needs a lot of work as far as behest, leves, and general mobs go. It was great in the alpha but the game has changed a lot since then. If you want to level faster id recomend goinng to Thanolan (Uldah area) and hanging out at camp dry bone, untill level 16 or 17 killing marmots coblyns and dodos. After that move to Camp Horrizon to do behest and leve quests ( Id recomend joining an LS or finding a group to do leves with as they are the best way to get SP)

If you are looking to get some super fast exp (physical levels) id recomend leveling other jobs just outside of Gridiana, when I go outside and just kill mobs it takes me about 1-2hrs to hit rank 10 on a job and I gain a ton of exp boosting my physical level. Crafting is another great option for boosting your physical level.

To get to Uldah area take the boat in Limsa (its free atm) this will drop you off in West Thanolan, and its not to bad of a jog to get to Uldah.