Upgrades of ratings on structured finance products hit an all-time high in 2015, according to a study released this week by S&P Global Ratings. The study tracked ratings across sectors and the world, while the U.S. residential MBS sector showed mixed performance. S&P said it had 30,359 ratings outstanding on global structured finance securities at the beginning of 2015. During the year, 9.8 percent of the ratings were upgraded. The rating service said upgrades in 2015 were most prevalent on structured credit deals in Europe and the U.S. Some 11.2 percent of S&P’s ratings were downgraded...