Office apps (Word,Excel...) slow over other networks

Hello

 

I have this weird problem where any apps from Office 2013 (Office 365) is slow to open outside our network (lan).

It happen on every laptops (+ 10 laptops)

  

if the laptop is not on any network, no wifi, no lan, Office apps are very fast like if they are on our lan

 

the problem is easy to reproduce, start Word on a Wifi network, it can take up to 30 second to load, disconnect the Wifi and Word start immediately

 

happen on different versions of Office 2013

 

Any help will be appreciate

thanks