A U.S. design patent lasts 15 years from the date it is granted.
Unlike a utility patent, which protects how an invention works, a design patent protects the ornamental appearance of an article. The term is measured from the grant date, not from the filing date.
The 15-year rule applies to design-patent applications filed on or after May 13, 2015, when the United States joined the relevant Hague Agreement provisions. Older U.S. design patents generally had a 14-year term, which explains why some references give a different answer.
A design patent does not protect every aspect of a product: its claims are directed to the illustrated visual design. Utility and design patents can sometimes protect different features of the same product, and they may be pursued separately.