15 dollars a day is a lot of money. Thats 105 a week. That's a lot of food for just one person to eat. If you dont mind cooking buy chicken thighs or drumsticks, 1lb of brown rice for a buck, 1lb of beans for about a dollar. 5 dollars on vegetables(carrots, spinach, celery, tomatoes, 1lb of brocolli). Shop around don't just go to one grocery store or look through ads you get in the mail. Stores usually have good deals on the weekend. Go to the store with a list and plan. Also keep track of the items youre buying as you put it in your cart it's real easy to go over. I know it's basic stuff put I had to learn it the hard way.
If you don't want to cook, check out the prepackaged frozen dinners have those with some fruit.