I can play Stairway to Heaven's solo for the most part. Except this part. I have no damn clue how to position my fingers.
Keep your middle finger on the 14th fret on the fourth string, and first and third fingers ready on the second string, then do as shown repeatedly. Just bend downwards not upwards. It's more difficult upwards, but I do it downwards and it sound the same.
I usually use the index for the 13th fret and then middle for both the 15 fret bends and the 14th fret on the third string (I bend it upwards but by using the middle for both you can be sure the bend won't get in the way of the 3rd string notes).