The 15' has a single layer of
fiberglass. The 16' has two.
Attached (I hope) is the 15 ft spec sheet we were sent when we bought our 2016 Parkliner -which has held up very well. I think in this day and age the quality of the Parkliner looks better and better and better.
One complaint on the original model - the hinges on the door. I found that I could
paint them with spray flexseal
paint and they hold up fine. Aaron -the Parkliner Team Leader, gave me that tip.