Database: beer_factory
Question: Which brewery brewed the most sold root beer in 2015?
SQL: SELECT T3.BreweryName FROM rootbeer AS T1 INNER JOIN `transaction` AS T2 ON T1.RootBeerID = T2.RootBeerID INNER JOIN rootbeerbrand AS T3 ON T1.BrandID = T3.BrandID WHERE T2.TransactionDate LIKE '2015%' GROUP BY T3.BrandID ORDER BY COUNT(T1.BrandID) DESC LIMIT 1