Reporting Services is extremely slow, and executing a report in HEAT can take up to a minute.
It occurs not only with HEAT but also opening the SSRS website independently, for example accessing the SSRS url in http://localhost/Reports (or any other configured).
The antivirus could affect the performance of SQL Server Reporting Services:
1.- General exclusions for SQL Server
2.- Specifically for McAfee VirusScan: URL Exclusions (adding the URL used in HEAT)