Just finished the quest where I got my adventurer stone. This is for LDoN correct? I am level 15. So whats next from here? Am I ready to go for LDoN when I hit 20 now?
Yes. Technically, you don't have to get the adventurer stone to participate in an LDoN adventure. The stone allows you to use the magi at the camps to transport around (which is super worth it by itself). Once you hit level 20, you should be able to join LDoN adventures.