Since this is an interior scene with windows being the primary light source, you will want to use a feature called *Light Portals*.

Basically, you add an area lamp into each window, align it so that the plane of the lamp is in line with the plane of the window, scale the lamp up (using the size value in the lamp settings) to be the same size as the window, and then check the *Portal* option that is also found in the lamp settings.

These portals help Cycles figure out where the light is coming from, and can greatly reduce noise.

Here's a good video that goes over setting them up and how they work: https://www.youtube.com/watch?v=1LjLyTBbl6s.

**EDIT:** Here's an actual comparison of your scene. I added a portal at each window/door/skylight, and used the exact same settings as you had. The only difference was that I changed the dimension scaling from 200% to 50% and the samples from 2000 to 50, just so I could do this quickly.

Here is with no Portals and 50 samples. It took 38s to render on my GPU.

[![enter image description here][1]][1]

Now here is the result with a portal at each light source (even the ones outside the camera view). It took only 4 seconds longer at just over 42 seconds.

[![enter image description here][2]][2]

And I think those results speak for themselves... :)

Here's the file too if you want to look at what I did. You will have to relocate the HDRi though, as I had to set it to a different path on my system.

[<img src="https://blend-exchange.giantcowfilms.com/embedImage.png?bid=4779" />](https://blend-exchange.giantcowfilms.com/b/4779/)

  [1]: https://i.sstatic.net/79XYc.jpg
  [2]: https://i.sstatic.net/8tsH7.jpg