The Champ just doesn't have the power to combat more than a light breeze. Adding weight won't help. What you need is more power. Your best bet is to upgrade to a larger, more powerful airplane. Colorex's recommendation of the Bixler is a good one. I've flown similar airplanes in winds WAY over 15 mph!
You CAN control the Champ in moderate winds (10 mph or less) but, it will fly backwards! With some experience, you can learn to use gravity to your advantage and fly in winds higher than you can at this time. For instance, If you are downwind and need to gain ground, you can dive to pick up airspeed. But, again, even a moderate wind will overcome the ability of the little Champ.