Sounds like you had some fun
I had a similar experience when I got my first boat, although mine ended with the boat on top of a cement dock!
Your C15 should be a fine starter boat, but learning in 12-15 solo is not ideal, although you will learn fast!
First off, be safe, don't sail solo in those kind of winds until you have a little experience. Sailing under the main alone usually works good in a dinghy. Sailing under the jib alone, as is sometimes done in keelboats, usually results in loss of helm control in a dinghy (that's how I ended up on the dock).
Go out in nice calm winds, say 5kts or so. If the boat starts to heel too much, ease the main and/or bring the bow to windward. Once the boat flattens out, fall off a little to gain some speed and repeat. Resist the natural tendency to fall off (turning downwind) without easing the main, this will cause the boat to heel even more as the sail gets perpendicular to the wind.
If you want to hold a steady course in gusty winds, follow the pattern of "ease, hike, sheet". In gusts, you will probably not be able to hike fast enough to flatten the boat, as quickly as you can ease the main. Once the main is eased, the boat will flatten out, then hike out to windward. Now that you have more "ballast" to windward, you can start sheeting in the main to pick up speed.
Try to avoid sharp jibes (bringing the stern across the wind) that involve turning the boat close to 180 deg, from close hauled to a run. A small boat, sailing under the main alone, will want to round up...fast, and could send you for a swim (err...done that too). Instead do a "chicken jibe" to turn around, by tacking and then continuing to fall off the wind, keeping the boom on the same side as it was after the tack. This will prevent the boom from wildly swinging across the boat. No shame in the chicken jibe, I have done them many times, and still do, if I think the conditions are getting out of hand.
Capsize your boat. You need to learn how to right the boat, as you probably will capsize at some point anyway. Better to do this the first time in a controlled situation, than in a freak storm. Of course, only attempt this if help is close by or you are close to land.
Get some instruction if possible. Check your local yacht clubs, marinas, parks and rec departments, etc. Often they will have classes for a reasonable price. You will learn a lot and be able to sail with others, so if you need help, you won't have to get a tow from the harbor patrol.
Check out the C15 class website and the yahoo newgroups (there is probably one for your boat). This will put you in touch with other sailors of your boat and you can probably find someone in your area to go out and show you the ropes.
Have fun on your new boat,