I find the 15 to be the do it all bottling within the VW line. More refined than the ORVW 10/107, more bold than the 20. They all bring something unique. I find that my favorite varies with mood and palate. Anymore I lean toward the 10, some wood, but the bourbon is the star. The 15 takes that and ramps up the wood. I tend to love the elegance of the 20, but less often. By price it is an occasion pour, but to me, it is an occasion pour because of its flavor as well.
I just had a nice pour of 15 last week. Compared to the older bottlings, I get a little less brown sugar, a little more cinnamon, and a little more heat. My perfect pour of 15 would be a combination of the brown sugar and cinnamon without the perceived increase in heat.