Only a guess. I get the impression you might have recently downloaded and installed Spybot, for the first time. And when trying to update for the first time, it took 15 minutes. If I'm incorrect, please disregard my post and I'll take my guesswork elsewhere.
If it is the case, I would wait until next Wednesday, when Spybot updates again, before considering this a problem. You could wind up going through a lot of unnecessary steps, when in fact, it may not be a problem at all. If Spybot isn't giving you problems otherwise, why not wait the few days to confirm it.
Next week you might want to choose a different mirror site to download the updates from. Seems as though, everyone has their favorites, and it takes time to establish which site/area works best for you. It shouldn't take 15 minutes, no matter where you go. Or at least in my opinion, it shouldn't.
Just something to consider. I wish you the best of luck, whatever you should decide to do.