Bengaluru, Feb 2: India's third largest IT firm Wipro Ltd has set a revenue target of $15 billion from its global IT services business by 2020, with 23 percent operating margin, a top executive said on Tuesday. "As detailed to you all recently, our ambition is to double our size and touch $15 billion revenue with 23 percent operating margin in four years ," Wipro's new chief executive Abidali Z Neemuchwala said in an e-mail to his employees on taking over the top post on Monday.