Question: In what year did the resort where UFC Fight Night 80 was held open?
Sentence (from "UFC Fight Night: Namajunas vs. VanZant"): UFC Fight Night: Namajunas vs. VanZant (also known as UFC Fight Night 80) was a mixed martial arts event held on December 10, 2015, at The Chelsea at The Cosmopolitan in Las Vegas, Nevada.
Relevant evidence: Yes