I created two lights using planes and tried to use them to simulate area lighting inside and outside the room. I then used a sphere to create a shadow casting light as if something really bright was on the other side of the door way. For some reason I always get noise if I use more than one lighting object. I tried using the denoise option but it still looks bad.
Using denoise alone is not a solve all solution. There are other techniques that must be used with it in order to get the best out of it.
First would be to reduce the number of light bounces from any light sources in the scene. Also making light sources larger for any lights that will be off camera helps as well.
Changing the sample seed and light sampling threshold will make a difference. Maybe not much, but every little bit helps. Clamp direct and clamp indirect will also help to reduce the noise, but setting them over 16 may produce unwanted results.
Render samples are important when it comes to using denoise. Too few and it will cause artifacts in the render. For a scene like this, 500 tends to be a good starting point. The more samples, the better the render will look.
For more information, there are countless tutorials on YouTube about how to get a cleaner render.
In your first image, your preview render is set to only 10. That might be why there’s a lot of noise in the scene.
Set light bounces to about 3 or 4 and out your samples way up, then try bringing samples down until you find a happy medium 
And yes you could try clamping indirect lighting, sometimes that helps get rid of fireflies.
The preview was set to 10 because I was following the suggestion in the exercise. The image though is from the the render which should have been 128 samples. I will try playing with some of the other setting you pointed out.
