We've published a small but significant performance update for PTS that includes optimizations related to physics processing that should help with the hitches some players experience in particularly large fights (60+ players in an area). The code changes were significant, so we're hoping to see concentrated pops on PTS over the weekend to ensure there aren't any major issues at scale before we publish to Live servers.
There are still further optimizations on the horizon, but this round of changes should significantly improve your performance while in combat with concentrated groups of players.
Will leave this thread open for feedback over the weekend!
Source: Test Server: Announcements