Thingworx slowness

In general I would say no.

Slowness is dependent on many things, however if you are experiencing slowness by logging in with the same user on several PCs,

then something might not be right in the way the application is designed, if you are doing it all from the same ip, it might be a throughput impact,

or there is some strange new bug.

Only if you have a webpage open for each of those sessions, and this webpage contains an AutoRefresh widget, which triggers some heavy processing on the server side frequently.