Your running the Editor + 2 clients. That’s 3 Renderings! So yeah it’s gonna run like crap.
In Editor Preferences → Play in Editor there are settings you can apply for testing.
If your going to use dedicated server (Client Mode) then just add a new entry for each new client.
If using Listen Server (client 0 is Host) then use the Server Fixed FPS and Client 0 will be the joining player.