After the 2nd or 3rd time starting a class you pretty much get the feel for how to do it quickly. Initially kill a few things, you'll be level 3 or 4 in no time flat. Check the hunting log and kill all of those things, do class quests, grab a leve or two if you find that you have a lot of allowances and you'll be level 15 in no time and ready to get into dungeons (or stop if you were only leveling to 15 for the quest prerequisite).