ZOHO CRM very slow from one location but not from another

ZOHO CRM very slow from one location but not from another

One of our clients is experiencing extremely slow response rates with their zoho crm account, yet when I login from my location my response rates are great. I'm on a mac using Safari, and they are using IE 11 and Trend Micro Virus protection software. Any ideas on how to speed up their response times?  Could it be the virus software?