Guys: the questioner asked the meaning of, or why the bugs are there. I think we are getting too technical and can't see the wood for the trees. Most of the answer have concentrated on only V2. What about the significance of +15?
if you have an engine failure between V2 and the all engines climb speed you should hold the speed at engine failure, and this includes any emergency turn below acceleration height. In this scenario reducing to V2 would do nothing for you, it would reduce your climb angle and bring you closer to the stall. Is the 737 operated differently to this?
This now widens the discussion. There was a DC-10 out of Chicago who had a catastrophic engine failure after V2, lost some LED's, reduced to V2 as per SOP's, stalled & died. They had a flying aeroplane!
I flew for an outfit that taught ET's were flown at V2. If you have an engine failure after V2 the FD holds that speed in pitch. If there was an ET the company expected you to ignore the FD, reduce to V2 and fly the the ET. IMHO, daft. Fly the ET but keep what speed you have. It will be between V2 & V2+15. The climb performance and turn radius will be a gnat's cock the same. KISS!