If you are 15mm gamer and have miniatures from different manufacturers, you may know about size difference in this scale. The matter is some manufacturers made true 15mm figures, and other 16mm, 17mm and even 18mm figs. Peter Pig is one of my favorite manufacturer, but his true 15mm figures looks a bit small in comparison to Blue Moon and Irregular Miniatures figs.
Here is size comparison shot of "Blue Moon" Wild West range civilian, "Peter Pig" Sudan range British soldier and "Irregular Miniatures" Colonial range Sepoy. As you can see true 15mm Peter Pig guy is on the smaller side.
But I found a solution how to deal with this size difference!!!!
You just need to use greenstuff or other material to uplift your true 15mm miniature from its base. When basing your bigger 15mm miniatures, try to cut their base to minimum and place figure inside the washer hole to make miniature look smaller. If you don't use washers but coins, just try to make your uplifted smaller figure heads to be on same lever as bigger 15mm guys.
Here is photo of uplifted Peter Pig figure, true 15mm Wild West figure with sanded base (sorry I haven't finished painting this guy) and bigger Blue Moon figure (with cutted base) placed in the washers hole.
Hope this article will be useful for you :)