Will vetted node affect the vetting speed of the new node on the same IP?

I know that traffic is shared between nodes on the same IP and that unvetted nodes only get 5% of possible traffic. So if I already have one vetted but not full node and start a new one on the same IP address. How will they affect each other? Will traffic on vetted one drop to the levels of unvetted or will the new one become vetted faster due to increased traffic from the vetted neighbor?

When your node is in the vetting phase the potential ingress traffic is taken from the 5% pool. The fully vetted but not full node will get potential ingress from the 95% pool. So they are effectively treated as separate during vetting, and there will be no difference to either of your nodes until the second one is vetted. Keep in mind that vetting is on a per satellite basis.