yea, I doubt there will be 15 eras, it would be too intensive since Empire Earth was about civilization, Spore is more than that.
At the least I'd expect there to be a tribal era, classical or medieval, and finally modern. I know WW is probably trying to keep the stages as simple as he can, but I can easily see bronze age and iron age (which the classical period was partly in) incorporated into the tribal age at first then same in the city stage, then I guess the medieval era or whatever equivalent, then industrial, then modern/technological.