To Notso Fantastic
Thank you for answer.
But I am interesting to know - why?
May be NG VREF 15 is more close to stall, than VREF for other flap setting?
For example, in case of LE FLAPS TRANSIT on the Classic 737 we should set VREF15+5
but on the 737-800 we should set VREF15+15 (10 knots more)