Iray Preview will give you your full light solution if it is blending into photoreal. If you just want to mess with Spotlight placement, Switch your blend mode to interactive, and depending on your hardware, you may also benefit from setting your final render to interactive during preview. If your hardware is not good enough to work to a degree you are happy with in the main viewport, you can, instead, set the aux viewport to Iray mode. Setting both to Iray will bog down your system, regardless of hardware, and is definitely not recommended.

You can adjust your settings, except for setting the final render to interactive (Render settings pane), in the draw settings pane. Set it to best fit with your hardware.