Here is a strategy that may save you some headaches, though it won’t necessarily reduce your simulation time.
Because you have such a large number of light sources in your electric lighting simulation, try running multiple renderings, each containing only a subset of your light sources. Each needs its own ambient file, of course. The individual renderings will run much faster than a single rendering containing all of the fixtures, although the total rendering time won’t change much.
This has two advantages. First, you can get preliminary results much faster, and if you find an error in a group of lights, you need rerun only that group and not the entire simulation. Second, you can use pcomb to sum your images in multiple ways, allowing you to generate different combinations of daylight and electric light, or different dimming configurations of electric lighting, as a post process to your rendering.