MZ73 - I only flew classics so I can't comment on any variant of the NG - The LE slats extend to full passing flap 5. Flap 10 is a valid configuration for flight with gear up.
In all my time flying 737-2/3/4/5 we always had FDM - I always called gear dn/flap 15 at the same time (But only from Flap 5 - this was as per SOP - we did however pause between selections) and never had an issue with our flight data monitoring folk.
Personally, I feel you fly the aircraft to the SOP's. If the FDM folk get alerts from pilots flying SOP's, then the FDM program needs reprogramming, not the SOP's changing.