Hi,
I don't know about the expected latency, but I do know that the latency is indeed noticeable. We had an installation where, because os some crazy routing requirements, the calls had 4 legs in our system instead of 2. In that case the delay was really noticeable.
The situation improved considerably after we used "Receive only RFC 2833 mode".
Please check "13.2.5 Setting Receive-only RFC 2833 Mode" in the ip_media_api documentation.
Chris