MacOS – How to prevent document preview over slow connections

If the issue is not common enough to find a solution on the Apple Knowlegde Base then it is most probably a rare issue caused by a corruption in the operating system or a 3'rd party application. Under these circumstances I would recommend one of the following:

• Reinstalling OS X (after performing a backup, preferably with Time Machine).
• Find someone else with identical hardware and software to see if their laptop does the same thing under the same circumstances (might be a compatibility issue with your wireless access point or router?)
• Make a reservation at the Apple Genius Bar, they are great troubleshooters and will be able to tell you if there is something wrong with your laptop hardware or software.
• A lot of troubleshooting information can be written to the OS X Console. Just have it running (and visible) while replicating this issue and it might print some information related to the issue.

I hope one of those steps can help you diagnose the issue, as it does not seem to be common enough to find a single solution for :-)

UPDATE: Since it appears that you are running "ADMitMac" which probably integrates with OS X in a significant way, and considering your issues are network related, there is a rather large red flag surrounding this software. I would strongly recommend uninstalling it as a trial to diagnose the issues you are encountering.

Usually, Bonjour only works on the local network and only its extension Wide-Area-Bonjour works through VPNs. Did you configure your Computer to use that or did you setup your router to handle that? Also, which other resources appear for the others at work?

But anyway, you don´t have to have File Sharing "turned on" on your computer (which will then cause the broadcasting of your computer´s name over Bonjour) to access others, so just turn off the services you don´t want others to see and you should be good.