May I ask why you are shooting in manual mode? Auto ISO works well with flash and in my opinion aperture wide open means to narrow DOF (unless that is what you want) and risk for blur is too high with 1/15-1/30s unless you AND your subject is very steady AND you use wide lens.
I also most often use Aperture mode but try not to set less than f8, almost never more than ISO100-200. If you always shoot wide open, IMO Auto mode is better. Camera always tries to widen the aperture and if that does not work than raise the ISO and lowers the shutter speed. Isn't it so?