Outlook 2011 with office 365 shared calendars extremely slow + crashes

Problem:

Each user needs to see multiple shared calenders.

We can add them without a problem, but it turns outlook 2011 in a real nightmare, slow responds and crashes.

If we remove the shared calenders, the problem is fixed and outlook works fast again.

We have this problem since we migrated from an onsite exchange 2003 to Office365 and Outlook2011, with the onsite exchange there was no problem.

It works perfectly on windows7 with office 2010 but all the Mac computers with outlook2011 are working so slow they constantly crash.

Is there some way to solve this, seems to me that calendar sharing is a basic function.

The Mac machines all have 8 GB of RAM and an up to date office2011.

I hope anyone can help.

Thx