Well, Plynkes is correct - mostly. I am working in 15 mm and using the Blue Moon range of Boxer buildings (mostly) and their figures plus some from Old Glory 15s, Lancashire, and the defunct Cell Mate Miniatures.
As to changing up, I have so much in 15 mm that it would be an odd move to do any other scale. However, I have been toying with a smaller scale for the Seven Years War but I doubt I'll make that move just because I have too much already and need to downsize what I own. And, if it comes to it, I might go with 40 mm figures if eyesight becomes an issue one day.