Reducing noise in interior Scenes caused by many lights using Cycles As mentioned in the title of this post I am just struggling with the noise in my render result. I am not talking about fireflies, I am talking about actual noise.

I read a lot about how to improve the result by increasing the amount of samples and stuff, but for the following result I already sampled the image 2500 times. 



As you can see, the scene is quite simple. I modelled a room with multiple spotlights in the ceiling. 



In full resolution I have a lot of noise in the darker areas, even after 2500 samples.

The target of the project is to make 3-5 sec camera animations, that lead from one hot spot in one room to another (the showroom isn't finished yet btw).

This image took me about 12 minutes to render on renderstreet. And regarding the finished project, it would take me about 74 hours to render only one animation with this noisy result.

So my question is, how can I get a cleaner result with less samples, so it will render faster?

I added my .blend file for you to download. I deleted the glass stuff in the middle of the room because I want my client to be anonymous).

http://www.file-upload.net/download-9405390/main.blend.html

Thanks in advance!
-Marten
I guess, that you know most of the common tricks. But here are some tricks that I often use:


Make a hole into the building outside of the cameras view of field
Increase the resolution, decrease the sample rate and resize the image afterwards. This will make the image softer, but if you double the image size, and render with a low sample rate and resize the image afterwards, the noise is evened out (I was able to render an interior architectural scene with only 5 samples)
Enable a small amount of global illumination and increase the shadows afterwards with the Compositor