I only fly the 737NG, so forgive me if I speak out of place.
the min speed to retract from Flap 40 to flap 15 was when the airspeed had reached Vref plus 15
I agree with
Rainboe. On a standard app, you would be flying Vref40 + 5 anyway. When the decision is to Go Around the standard call is “Go Around, Flap 15” In that time, although TOGA has been pressed you haven’t increased your airspeed by 10kts, so why in this situation would you wait till Vref40 + 15 until you retracted to flap 15?
If below Vref however, I don’t think I would ask for the flaps to be moved until I had got the speed back to Vref.
Just my thoughs……