MADRID, Nov 15 (Reuters) - Spain’s BBVA on Monday said its board had agreed to launch a voluntary takeover bid for the 50.15 percent stake it does not own in its Turkish lender Garanti BBVA, with a price of 12.20 Turkish lira ($1.22) per share. BBVA said that the price offered represented a premium of 34 percent over the volume weighted average price of the past six months. The transaction could be worth 25.70 billion lira, BBVA said. $1 = 10.0153 liras Reporting by Jesús Aguado; editing by Inti Landauro