Question: Riviera Holdings Corporation owned a casino In Nevada which operated until what year?

Context paragraphs:
MiTAC Holdings: MiTAC Holdings Corporation, through its subsidiaries (MiTAC International Corp.  and MiTAC Computing Technology),provides GPS navigation devices, automotive solution, cloud services and cloud computing products worldwide.The company offers a range of electronics manufacturing services, such as research and development, design, manufacturing, assembly, marketing, and solutions.It also distributes portable car navigation products, outdoor handheld navigation devices, and mobile GPS solutions; and DashCam for vehicles, portable navigation devices for 4WD, and trucks under the Magellan, Mio, and Navman brand names.In addition, the company designs, manufactures, and markets x86 server/workstation platforms to OEMs, VARs, system integrators, and resellers under the TYAN brand name.  Further, it offers storage products, cloud computing applications, all-in-one PC, thin client, and POS system, as well as smart wearable device and professional tablet series.  MiTAC Holdings Corporation is based in Taipei, Taiwan.

Riviera Holdings: Riviera Holdings Corporation is a defunct casino operator that was based in Winchester, Nevada.  It owned two casinos: the Riviera on the Las Vegas Strip, closed in 2015; and the Riviera Black Hawk in Black Hawk, Colorado, sold in 2011.

W. Bruce Johnson: W. Bruce Johnson was the interim President and CEO of Sears Holdings Corporation, the parent of Sears and Kmart, from January 2008 to February 2011.  Mr. Johnson served on the Board of Directors for Sears Holdings Corporation from May 2010 until May 2011.  From July 2012 until August 2015 he served as President and CEO of Sears Hometown and Outlet Stores,Inc. Mr. Johnson served on the Board of Directors for Sears Hometown and Outlet Stores, Inc. from July 2012 through May 2015.

Eugenio Lopez III: Eugenio Gabriel "Gabby" L. López III, (born August 13, 1952), is the current chairman of ABS-CBN Corporation, the largest entertainment and media conglomerate in the Philippines, with investments primarily in television, radio, cable telecommunications, and film production.  He is also director and treasurer of López Holdings Corporation (formerly Benpres Holdings Corporation).

Riviera (hotel and casino): Riviera (colloquially, "the Riv") was a hotel and casino on the Las Vegas Strip in Winchester, Nevada, which operated from April 1955 to May 2015.  It was last owned by the Las Vegas Convention and Visitors Authority, which decided to demolish it to make way for the Las Vegas Global Business District.

America West Holdings: America West Holdings Corporation was an Arizona-based company whose primary holding was America West Airlines.  On May 19, 2005, America West Holdings Corporation announced it would acquire the Arlington, Virginia-based US Airways Group.

Mitsubishi Chemical Corporation: Mitsubishi Chemical Corporation (三菱化学株式会社 , Mitsubishi Kagaku Kabushiki-gaisha ) , or MCC, is a subsidiary of Mitsubishi Chemical Holdings Corporation.  It was a Japanese corporation, that merged with Mitsubishi Pharma Corporation in 2005 to create Mitsubishi Chemical Holdings Corporation.

Fabrizio Boccardi: Fabrizio Boccardi is an Italian American entrepreneur, investor, and producer.  Boccardi is the owner and creator of the multimedia brand the Tyrant.  In addition, he controls several investments,including Media, technology, and Gaming in the United States and abroad.  Boccardi has attempted to buy control of a Las Vegas casino, most notably Riviera Holdings, former owner of the Riviera Hotel & Casino on the strip of Las Vegas, and Riviera Casino in Black Hawk Colorado.

Lopez Group of Companies: López Holdings Corporation (formerly Benpres Holdings Corporation) is a Filipino business conglomerate founded by the brothers Eugenio López, Sr. and Fernando López.  It is a major player in the public service and utilities sector in the Philippines and serves as the López family's publicly listed holding company for investments in major development sectors such as broadcasting and cable; telecommunications; power generation and distribution; manufacturing; and property development.  It added to its portfolio investments in other basic service sectors but has also since sold its interest in banking, toll roads, information technology, and health care delivery.

ABS-CBN Philharmonic Orchestra: The ABS-CBN Philharmonic Orchestra is a Philippine broadcast orchestra based in Manila and is operated by ABS-CBN.  The orchestra was founded in 2012, Gerard Salonga served as the orchestra's conductor and musical director.  It is a joint venture of ABS-CBN and First Philippine Holdings Corporation, both under the portfolio of Lopez Holdings Corporation.  The orchestra consists of 40 instrumentalists.  Famous Filipino composer and conductor Ryan Cayabyab lauds the orchestra for its smooth and beautiful music.

Supporting paragraphs: Riviera Holdings Riviera (hotel and casino)
Answer: 2015