At your level you can do lots of quests, some of those quest give you 3k sp and are so easy to do. The Grand Companies quests all give you 1500sp, and 1000 sp when you talk to the guy who sells items in exchange for seals for the first time. While this isn't like a main leveling method it does give you a huge about of extra sp on the side. Grinding seems to be equalized to 200 sp a mob in the right level range, leading me to think they will for sure give us exp chains on mobs, to have exp chains you need a base sp system anyway. So in future updates open world grinding may be possible. Once you hit 38, or 40 I don't know what you'll do, we haven't figured it out yet, used to be failing leves was the only real way to get passed this hump, the raptor grind camp will always be open I guess.