I guess there's also a difference between using a 4200rpm 1.8" notebook drive and a 10krpm desktop raptor. New drive, full drive, SSD drive, totally fragmented drive - 15 seconds can mean anything without more specific details.
Some machines work great out of the box (laptops), then after I load all my apps and am ready to actually do things it slows down to a crawl. I remember working with one XP laptop that took 4 minutes to boot because some driver/service conflict at startup froze the damn thing for almost 2 minutes. I never could figure out exactly what it was.
I've seen rogue software wreak havoc with the registry to the point where it would require a reinstall or backup-restore to fix the problem.
Microsoft has yet to revolutionize the windows registry, give users tools to easily diagnose and repair problems with it or keep it running at top speed. Just eliminating the registry altogether would solve A TON of problems.
But hey, 15 seconds still beats having to take a dump after you hit the power button...