16 levels with PC wealth would be CR 16. On top of that Vampire is a +2 CR Template, and Advanced is +1, so based on that, it would be CR 19. However with 25 point buy, that's 10 more than the "heroic array" traditionally given to NPCs, so I might say that's worth an extra +1 CR, depending on how optimized the points are distributed.
Edit:
PC level wealth is tricky, as is the 25 point buy. Normally neither of these would quite be CR +1(emphasis mine). Taken together, though, yeah probably -- especially if you're optimizing the build. For instance, building vampires around classes with high Cha, like sorcerors, can give crazy results because vamps get their hits boosted by Cha instead of Con. Giving PC wealth can pile further on this with Cha-boosting items.
Technically this is incorrect, according to James Jacobs:
Fair enough. Their lack of wealth would definitely decrease their CR, but I still don't see why they didn't keep the original wealth what it was for like boss characters. Especially if you're doing it as a fast progression, which states you go one level higher for wealth, and it's STILL lower. Unless you're supposed to go PC wealth table for them. Or half and half???
I'll throw this one in there too. If the character is an Aristocrat 9/Fighter 6, what's their total wealth?
For boss NPCs, just give the NPC a PC's wealth. That increases the boss NPC's CR by +1, so a zero HD creature with class levels and PC wealth is a CR equal to his class level.
We do this pretty much for EVERY major boss of an adventure path.[...]
Advanced template is +4 to all stats and +2 nat ac and is only +1 cr. There is no way a 25 point buy makes that big a difference. It is trivial.
PC wealth with class levels CR = Level. Vamp +2. Advanced +1. 16+2+1 = 19
It is CR 19