Does Camera Power Consumption Lower Without Output?
It's imposible to be sure without handling the actual hardware,
and difficult to guess without seeing the data-sheet of the camera.

I would expect the presence of the light to increase the power draw of the system. 

It could be that running the light increases the draw to 1.5A + 0.75A = 2.25A or it could be that the camera itself draws 0.75A and the light when present brings the total upto 1.5A