The connection to Chicago is much worse than Las Vegas (LV looks normal considering you’re connecting from OCE). Unfortunately, if you’re in a group where the leader is on a Chicago realm, you’ll experience increased latency.
There have been some complaints about Twelve99’s increased latency on their routes, but there’s nothing you can personally do about that other than focus on playing only in Las Vegas-based groups. For instance, I try to avoid groups on OCE realms because I cannot play on 380ms+ ping from the Southeast US. You can use this site to see where each server is located:
Note: Los Angeles servers relocated to Las Vegas. That site is a bit out of date in that respect.