The chances are that if you push the throttles to the stops while selecting flap 15 and then get select the gear up you will have built up so much inertia in the aircraft that you will fly past a 1500 ft missed approach altitude, one click on the TOGA button gives a reduced GA power that makes the whole thing more manageable, two clicks will give you full GA thrust if you should want it.
That is true if you are doing a coupled approach to touchdown with AT engaged. But probably the vast majority of 737 landings are conducted with a manual landing with the AP and AT switched off. That being so, there is no point in hitting TOGA on the GA since you still have to manually push open the throttles to climb away and all TOGA does then is give you FD GA bars which you don't need anyway unless you are incompetent at flying without the crutch of a FD.