Molly, I will start by saying 1.5mm is really small and there are many things it could be so I will send lots of prayers your way and good thoughts your way that it is not lung cancer. If it is then hopefully you are catching it at a very early stage. I have met quite a few people that had surgery to remove an early lung cancer and are doing fine, 15, 20 and even 30 years later. Some had chemo and or radiation but some did not.
As for how much could it change in 30 days? If it was small cell lung cancer it can change alot in 30 days as that is an aggressive cancer. Non small cell it is hard to say as some seem to change fast but most are slow growing. I would want my doctor to be aggressive and not be taking a lets wait and see approach as it could be my life at stake so be glad your doctor is that way.
It could be a scar from an infection, a fungus here in California Cocci is a fungus that gets into the lungs, my dad has a small nodule that is an old TB scar or a handful of other things. Keep us posted as you learn more as there are many of us here should you need us and we will all cheer when you tell us it is not cancer and many of us could use some good news

JanMarie