Hi Yusuf,
Your SCADUH guys are obviously unaware of the laws of physics. Usually the slowest thing on a SCADA network is their unpatched servers.
So if u have eliminated 90% of latency (what's a couple of milliseconds between PLCs/RTUs) u need to educate (re the speed of light thing) and get them tuning the app.
Do note that an architecture with minimal firewall traversal does help (eg one at the headend and a security oriented network fabric like mac in mac).
i have similar 15ms latency to (interstate) parts of the network and these (see link) guys look like they r running in AWS
https://medium.com/aws-enterprise-collection/reborn-in-the-cloud-talen-energy-s-journey-to-the-cloud... so i'd expect similar unless they're on top of an AWS campus
some latency commentary in here
http://trilliantinc.com/library-files/media/WP_Comms-for-DA.pdf
and a case study with latency issues
https://library.e.abb.com/public/8fe715f52164b564c1257c050041522c/008_Communication_en.pdf
IB