Class c ips aren't the answer. Google has more computation power than we can grasp. If they see 15 sites linking to one site with a spun article, they can easily map the rest of the network. You could do the same thing manually without knowing anything about the backend. That's the trouble with such high profile sites.
Add to that domain registration. A little piffy whois guard is not going to stop G seeing that all 15 sites are owned by the same person.