There are labor laws in every state that protect children (usually defined as people under 18 years old) from adverse working conditions.
Here are the child labor laws for Texas:
http://www.twc.state.tx.us/ui/lablaw/cllsum.html
15 year olds have a lot of leeway. Kids under 14 cannot be employed at all, it seems, except as "child actors".
14 and 15 year olds must meet rules about WHEN they work - i.e. you cannot work after 10pm if you are supposed to be in school the next day, and you cannot work more than 48 hours per week. A normal work week is only 40 hours so that's a LOT of work. You can work after 10pm during the summer.
Here is a quick summary of what you are allowed to do (click on the "source" link to get the full document - scroll down a LOT to get to the "allowed" section).
"A child who is 14 or 15 years of age may be employed in the following occupations in retail, food service, and gasoline service establishments:
Office and clerical work (including operation of office machines).
Cashiering, selling, modeling, art work, work in advertising departments, window trimming and comparative shopping.
Price marking and tagging by hand or by machine. Assembling orders, packing and shelving.
Bagging and carrying out customers' orders.
Errand and delivery work by foot, bicycle, and public transportation.
Cleanup work, including the use of vacuum cleaners and floor waxers, and maintenance of grounds, but not including the use of power-driven mowers or cutters.
Kitchen work and other work involved in preparing and serving food and beverages, including the operation of machines and devices used in the performance of such work such as, but not limited to, dishwashers, toasters, dumbwaiters, popcorn poppers, milk shake blenders, and coffee grinders.
Work in connection with cars and trucks if confined to the following:
Dispensing gasoline and oil.
Courtesy service on premises of gasoline service station.
Car cleaning, washing and polishing.
Other occupations permitted by this section.
But not including work:
Involving the use of pits, racks or lifting apparatus or involving the inflation of any tire mounted on a rim equipped with a removable retaining ring.
Cleaning vegetables and fruits, and wrapping, sealing, labeling, weighing, pricing and stocking goods when performed in areas physically separate from areas where meat is prepared for sale and outside freezers or meat coolers."