I'm catching up on posts here and so this is a bit late.
Short story: I also much prefer 633 over 2015.
2015 was my introductory vaper and I once rated it an "A", but now it is a B/B-. 633 is one of three currently available vapers that I give an A+ to (Long Golden Flake and Escudo are the other two). I've been smoking 2015 aged over 3 years this past week. Nice to revisit, but my opinion remains true to my valuation of several years ago. I've a bit over 2 pounds in the cellar and doubt I'll purchase any more.
633 is richer, fuller, sweeter and has more perique (but not over-done to my taste like many popular vapers are). It has brown and golden virginias in it which has more of the nice hay-to-sweet grass flavors for me, along with the wonderful figgy taste I enjoy in my favorite vapers.
2015 has red (and... "orange"?) virginias and not as much perique. It is also stoved, which for me seems to lessen flavor components (I have a challenged pallet, I suppose). 2015 seems to have a bit more of a citrusy tang, which I seem to get more with red Virginia. But this is muted compared to say McClelland's 5100, I think due to a bit of stoving of 2015. 2015 is a nice smoke, but it seems rather on the bland side until about 1/3 way through the smoke and that is when the sweetness and the hints of fig seems to pick up.
Well, that is my take on these two blends, FWIW. As always, YMMV.