The team spent more than three weeks in the western German city of Duisburg working on the artwork, which includes a sandy replica of the Great Sphinx of Giza, Venice's Rialto Bridge and the grave of Elvis Presley.
It also features models of tourist attractions such as Athens' Acropolis, Barcelona's Sagrada Familia and the Leaning Tower of Pisa.
Guinness World Record official Jack Brockbank was on hand to approve the new record for the German sculpture, which eclipsed the previous tallest sandcastle, a 14.84-metre world peace monument built in India in February.
The team of international sculptors failed with a world record attempt last year and decided to use a different sand, mainly very fine quartz which is less than one millimetre in grain size.
"It did not collapse because the quality of the sand was better than previous attempts, the weather was good and very good planning," Ukrainian sculptor Eugenia Kolot said.
The castle will be on display until at least September 24 and the site has so far been visited by around 180,000 people, according to a local tour operator who organised the event.