Leveling a second class - lack of quests?

[Jaminos]

I was able to level my CONJ to 15 with relatively little issues, when I was leveling my second class required for Paladin. You only start running into problems if you want to level a second class past level 15. By then, your main quest is sending you all around Eorzea doing quests. While not required, you are encouraged to do every quest in that zone it sends you in.

So it leaves little for you to pick up later. But not really until after 15.