My very first Van Winkle bourbon was Pappy 20, and in hindsight I think it was really a mistake to start at the top. The Pappy seemed to program me for the taste profile I wanted. When I went looking for a younger, more lively Van Winkle and tried Pappy's younger siblings, they were good, but seemed to disappoint in a way.
Now that the Pappy 15 is around it fills the niche quite nicely.
That said, I've tasted ORVW 15 and Pappy 15 in a side-by-side and there were some times when I honestly couldn't tell them apart. From what I understand they are whiskey from the same batch, just selected for profile.