I think you are being a little optimistic about the amount of food you will be able to carry or you are underestimating the amount you will need.

To maintain your body weight under conditions of moderate exercise, you will need roughly 18 calories per day per pound of body weight. Assuming you weigh 160 lb, that is about 2800 calories per day. Your 15 lb of food, as described as mostly grains, should furnish 100 to 110 calories per ounce. Your 15 pounds of food will be 240 oz times (say) 110 calories per oz or 26,400 calories total. Dividing this by your daily requirement of 2800 calories gives you a 9.5 day supply of food.

I also think you are overoptimistic about the amount of food you can forage. Remember, you need to spend a lot of time finding food in the wild. You need an awful large pile of foraged greens to supply any calorie content at all. Yes, you can pick berries, in season, but a full cup of blueberries or blackberries will provide about 100 calories; are you ready to eat 28 cups of berries to meet your day's requirement? Trout will provide roughly 30 calories per ounce of uncooked fish. Enough trout to avoid weight loss would amount to about 93 oz or nearly six pounds. Hunting won't help much since carrying a firearm through many different legal jurisdictions can be complicated. And, a hunting license is required even to hunt squirrels; out-of-state licenses are expensive.

The last thing I want to do here is to discourage you from making the trip you are planning; I envy you the freedom. But, please take the reality of calorie requirements and the number of calories you can carry and find into your planning before you set out. You can easily start the trip with a well developed "reserve tank" or belly. Midriff fat contains 3500 calories per pound and will nicely supplement otherwise sparse rations. Hiking can be an excellent weight loss regimen but if you are already lean, you don't want to loose weight.