Switch back to daytime after finishing the Level 15 Destiny quest, and head back to White Sands to do the other knight Noah quests, killing the plant, killing Black Ones (if you had grabbed the necklace earlier you can escort Horensia to safety here as well.. saves you a trip back and forth.) The trick here is to quest your way about 1/2 thru 19.

Now you should have hit 20 at this point. At your homeland, talk to the smuggler nearby and head back to Tort-age.

When it loads, talk to the smuggler nearby again, and head BACK to your homeland. Once there, talk to the smuggler once more to go back to Tortage, yes it makes no sense, wait, that 2nd time, you get over 3k xp for that! Easy xp and should ding you 20 if you didn't already.

From there finish off any Tort-age quests if you like, or head off into the world, personally I finish Tort-age quests since I hate leaving an area unfinished, but that's just me, Plus at that point the Bat Demon quest is easily soloable, and nets you a blue piece of armor to boot(knight Noah).