Tons of stuff has changed. First, did you change the compatibility level on your database to 120? If not, you're using the old statistics with the new optimizer in compatibility mode, which might explain a difference in behavior, possibly. If you've changed the compatibility level to 120, then you've got an all new optimizer and a whole new cardinality estimator, which will seriously change the behavior of some plans. That, frankly, is the most likely explanation for many differences. Get the execution plan with the compatibility set to 110 and 120 and compare them.