15 people are the core team. 30 counting external personal.
The same aplies to Kunos or polyphony. Someone said before there are 3 modelers on Kunos.
I didnt dig in the 911 thing because like you say, it's very difficult to clarify if that 6 days was the time they took to model the car only.
But comparing the general figures, is nonsense how Polyphony take so long to develop their games compared not only with Kunos, but with the rest of the developers.
About Kunos, in an interview with Vasilakos he said modern cars are much more easier to develop than old cars because with old cars they dont have available telemetry.
PD: The conversation started because someone said that the explanation for Kunos taking only 6 days on developing the 911 model is because the 3D models on AC are poor, when this is very far from being true.