The tour sounds like a great ride. Go for it and have fun. I wish I had done my first tours at 15...
A few thoughts about your trip:
1. If you haven't ridden in years, you need to start training now. You need to develop the muscles you'll use for the ride and you need to build up endurance. This goes for everyone in your group. You're only as good as your weakest rider. If one of you isn't prepared, it could have some serious consequences for the rest of you. (Fortunately, getting in shape for a tour isn't all that hard and it's a lot of fun at the same time.)
2. As someone else has said, you need someone in your group who can make the repairs. And you need to have the tools and parts to take care of basic repairs on the road, especially for the times when you're far from a community with a bike shop. Have your bikes checked before your trip and on the road, give them a check each day before you begin.
3. Plan your route so you have places to stop for the night. Expect 100 kilometres or around 60 miles in a day for a respectable distance, especially if you'll have hills along the way. Also, when you're riding, pace yourselves. It's not a race. Take your time. Enjoy the scenery. Take breaks whenever you want. The ride is going to be at least as much fun as the destination.
4. Pack clothing for the worst weather you could expect to get. Trust me on this. I've learned it from experience. It's no fun getting caught in a cold rain without rain gear.
5. Because of your age, you need to take extra security and safety measures. Carry cell phones in case you need to call for help. Also, arrange to call home every day or two to let your parents know where you are and that you're all right. And most importantly, you need to arrange in advance your accommodations in Los Angeles and your routes in that city. Know the areas and streets to avoid. (The same is true if there are other large cities along your route.)