There are several things you can do to optimize a scene, mostly related to emitters.

- Make sure your emitting surfaces are as lowpoly as possible. Usually, a single sided Polygon will be sufficient.

- If possible, do not completely enclose your emitters inside a dielectric object.

- Make sure your Emitter is not intersecting other geometry.

- Very important: do not have very white or fully saturated materials in your scene. For example a completely white (255, 255, 255) material will take a very long time to clear and will also make the contrast in the image disappear. Also avoid completely saturated colors such as pure red (255, 0, 0). Pure white or pure saturated materials do not exist in real life so it's better to decrease the saturation a bit. For a white wall, around RGB 220 or less is sufficient.

- For interior renders where window glass reflections are necessary, use the AGS glass material for the windows instead of real glass. This will create the reflections but will not produce any caustics, thus speeding up the rendering.

- Perhaps you simply need more time for rendering, depending on your machine specs. Check www.benchwell.com to know how fast your machine is.