Hi Brittney,
A Walt Disney World vacation is great any time of year! I can't think of a better place to go during summer break.
In room babysitting is available at all resorts via an outside company,
Kids Nite Out. They offer in room babysitting as well as child care specialists to accompany you and your family in the Parks. They're available 24 hours a day, 7 days a week. Typically, they watch children ages 6 weeks to 12 years old. I'm not certain of the policy regarding your 15 year old.
All caregivers are: at least 18 years of age, certified in CPR and basic first aid, trained by Kid's Nite Out, have previous childcare or teaching experience, are thoroughly interviewed and screened.
I'm not certain if there is a time limit; however, there is a 4 hour minimum charge for in-room sitting services.
To contact Kid's Nite Out for more information, or to make a reservation, call (407)828-0920, 8:00 a.m. - 9:00 p.m.
Hope this helps. Have a magical vacation!