No, the Nano preview on the main page is fixed size. The preview in the Sky-Lab is slightly larger, and it is fixed size also.

My fix for this is I initially go to top menu File / Document Setup and whatever your default Render Resolution is set for, you can choose a reduced one from that list, These render rather quickly especially if you reduce to 50% or even 25% of your Desired final Image size.
This allows a quick review with the only draw back being you need to reverse this process.

Once I've gotten the scene layed out the way I want it, I increase the resolution because I do a lot of plop rendering through out the scene for testing purposes. My Final renders are done through "Render to Disk" method.

ICM

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Ockham's razor- It's that simple