Changing classes is completely up to you. At 15 you haven't done much with content so it won't affect you much, if at all. The thing to think about is many would consider Arc-> San the best solo class in the game. If you like solo play stick with it, if not change. I would recommend staying get with it long enough to get your mount. As for crafting, I started and leveled my main craft with my 1st job. It had some benefits but more drawbacks. I wouldn't start crafting till 1 job is at 50. On the other hand if you go culinary, do that now and take up a gathering class too.