I think you can narrow down a villain's tendencies fairly well after 15 hands though. Somebody showing 36/14 at 5nl is unlikely to be a nit, tag or lag for instance and unlikely to be competent, just like a 0/0 over 26 hands is unlikely to be lag, loose passive or completely incompetent.

The key is using the information at hand to make a better decision, rather than disregarding everything because of sample size.