Those samples in CoronaMTL are for rounded corners feature. They are irrelevant for any shading quality. LSM or UDH precision will not help you to clean DoF either, so set them back to default (LSM 2 and UHD precision 1.0)
What you need is simply balance AA rays and GI rays. Your scene is spending too much rendering time on GI rays, which take care of lighting, reflections, refractions and GI, but not enough time on AA rays, which take care of DoF.
So what you need to do is to decrease GI/AA balance to something like 4. Once you do that, and render, you will notice it will not improve quality, but it will make passes render much faster.
That's because now you are doing only 4 GI rays per one AA ray. GI/AA balance is basically amount of GI rays per AA ray, and Passes is basically amount of AA rays. Each pass calculates one AA ray per pixel.
So to clean up DoF, you need more AA rays. In Corona, AA rays are passes. So you need to increase passes to something like for example 256. But because you decreased how many GI rays are done for each AA rays, those passes will not take as long as they would take with 16 GI rays per AA ray. Passes will take less time, therefore in given time, you can afford to have many more of them. And many more AA passes mean cleaner DoF.
I hope i explained it well.
And the noise you have under your teapot is there because you enabled caustics in your glass material. The word "Slow" next to caustic checkbox is there for a reason ;)
