Depends where in Greathanc you are 15 Million Square Miles is a huge landmass to chart weather for. I imagine it would be reasonable cold; but it would be more warm that usual getting colder, as its moving into Winter and darkness for all but the a few furthur out and coastal Countries. Likely it would be lightly snowing, as always. Snow looks nice though; especially as all of it has been flatenned and its a huge city with large areas cut out for agriculture.
Haha, in all due time, in all due time... wouldn't mind hitting Eleventy-One-Hundred though, far more humourous number.