Try barring the 12th fret B and E strings with your index finger and rest your ring finger on the 14th fret G string.Thats the position you want to keep.Use your pinky finger to pull off the 15th fret B string.Dont take your index finger away from the 12th fret.If you can't make the bend with your ring finger,then...practice.I could tell you to just use your middle finger to do the bend and use the ring finger for the pull off if that would be easier for you,but then that wouldnt be proper positioning and might prove to be bad practice in the future.
That is actually a very,very common lick.