What's the fastest way to level?

[Niwashi]

I took me about four hours to hit lvl 3, and probably a solid fourteen hours to hit lvl 15. Granted, I wasn't very familiar with the areas before, and was still getting used to using a controller, but it still felt like an awfully long time.

That felt like a long time??? True, it's possible to do it quicker, but only if you forego any exploration or investigation of the story. You'd miss out on the best part of the game if you rush past all the content without taking the time to talk to all the NPCs, for instance. Slow down and the game will be a million times better for it.