I assume you realize that on Delta, a 14 year old MUST pay the unaccompanied minor fee. It is not an option.

Enrollment in the Delta Air Lines Unaccompanied Minor program is mandatory for children 5 to 14. If you prefer that your 15 to 17 year old travel without supervision, please advise the agent at the time of the reservation and it will be noted. Your child will be expected to handle boarding and deplaning as well as transfers to connecting gates on their own.
Remind your teenager never to leave the airport for any reason unless accompanied by a badged Delta employee or uniformed police officer until they have reached their destination city. She or he should never seek help from or leave the airport with strangers.
Provide your teenager with instructions, phone contacts and a small amount of money for food in the unlikely event their flight is missed, delayed, canceled or rerouted.
Remind your teenager that they can seek the assistance of any Delta employee if they have questions, concerns or need reassurance.
Remember most hotels will not accept young people who are not accompanied by an adult.