Viacom has extended its lease at 1515 Broadway in New York’s Times Square and is preparing to occupy the entire office portion of the tower after 2020, building owner SL Green Realty Corp. told Bloomberg today. Viacom’s lease will run through 2031. After 2020, Viacom will have about 1.6 million square feet at the building which serves as its headquarters. The agreement quashes speculation that Viacom — owner of the MTV, Nickelodeon and Comedy Central cable channels and Paramount Pictures — might leave Times Square after its leases expire in 2015. Projects seeking anchor tenants include the World Trade Center and Hudson Yards. Terms of the lease were not disclosed. The deal is the biggest U.S. office lease since at least 2008, according to data from CoStar Group Inc., a Washington-based real estate data service. Other large deals include Morgan Stanley’s lease of almost 1.2 million square feet at 1 New York Plaza plus two media deals from last year: NBC Universal’s renewal of more than 1.2 million square feet at 30 Rockefeller Plaza, and Conde Nast Publications Inc.’s 1 million-square-foot lease at 1 World Trade Center. Viacom currently rents 1.3 million square feet at an average of $61.59 a square foot from SL Green, making it the real estate investment trust’s second-biggest tenant, according to regulatory filing. The largest is Citigroup.