Outlook running slow and freezing

Hi all, 

I'm having problem on couple of computers with CRM 2015 Outlook add-in. On some computers its working fine, but on some its making Outlook to freeze, run slow, crash, etc. There is no rule on which computer this would happen, the one with high performances or low performances. 

I must emphasize that add in is used only for sending mails. In Diagnostics tool I disabled Outlook Synchronization option and enabled only Background Send Emails option.

Also, on some computers I added blank config file Microsoft.Crm.Application.Outlook.WebFormsHost.exe.config to C:\Program Files\Microsoft Dynamics CRM\Client\res\web\bin. This solved problem for some users.

Does anyone have any idea what to do to resolve this problem?

Thanks :)