Hi Ann,
Every time we would plan a trip to Walt Disney World when the kids were smaller we would have to go through the fleet of strollers to see what would be the best ones to take considering their ages.
I think your best bet would be to bring or rent a double stroller. You can
rent a double stroller at the parks. The Disney strollers are the easiest to push! If you think your 15mth old will nap then it might be best to bring a double stroller that the seat can recline back. Unfortunately, you cannot bring a trailer. Your 5yr old will likely want to walk most of the time.
I have 3 kids, and when they were in strollers we always had to bring two different strollers. Your best bet and easiest option will be a double stroller.
I hope this helps. If you have any other questions, please let me know.
Wishing you a very magical vacation!
Carrie