Why is my Scene Noisy at 5000 samples?

Here is an image of my scene at 5000 samples at 960x540.

I’m using volume scatter at 0.05 density in the world settings if that makes a difference. I have 2 portals at the front and end of the hallway.

Here is my blend file.

Please help!
Thank you.

Portals are used to “guide” light into the scene, e. g. an environment light into a closed room. Your environment is pitch black, so I’m not sure what you hope to gain from using portals…

Other than that, Cycles is not particularly competent with scenes like yours. Small light sources in a large room are kind of a nightmare scenario for any unoptimized pathtracer like Cyles. In a nutshell: Cycles fires rays from the camera into the scene and lets them bounce until a light source is hit. With tiny, bright light sources this can take forever to resolve, because the chance to hit a light emitter is so small…

You might want to have a look here.