The life-saving drug is used to immediately treat anaphylaxis, a potentially fatal allergic reaction to such things as peanuts, raspberries, milk, eggs and bee stings.
The laws allow schools to stock the epinephrine without a prescription for any individual student, a legal hurdle that previously kept the drug out of quick reach in schools.
The fifteen states, including Tennessee and Virginia, joined 11 others with such legislation already in place. Similar bills are pending in Michigan and Ohio, according to the Asthma and Allergy Foundation of America.
Only four states -- Maryland, Nebraska, Nevada and Virginia -- require schools to keep the drug on hand.
The most common method of administering the medication is through an auto-injector, known by the common brand name EpiPen. A spring-activated needle injects the epinephrine into the patient.
People with severe allergies that can trigger anaphylactic shock can die within mere minutes -- too quickly for emergency responders to be of help, in many cases.