Regarding this 'Flap15' rumour - maybe the co-pilot wanted a g/a and the Captain did not? Perhaps the co-pilot had been reading PPRune where I believe there had been suggestions in the past that the thing to do was either just raise the gear or select g/a flap?
In any case, if at Vref+5??, changing to Flap 15 would not cause an uncontrollable sink due to Boeing's manouevre speed schedule (power would help....). Far from ideal, mind you!