We have an internal web application and since short, it is very slow in IE11. Chrome and Firefox do not have this problem. We have an HTTP version of the same website, and this is fast with up to 6 concurrent HTTP sessions to the server and session persistence. However, when we change to HTTPS, all this changes. We still have session persistence, but only 2 simultaneous sessions to the servers and each request seems to take ages. It is not the server response that is slow, but the "start" time before IE11 sends the request (and the next request). The connection diagram changes to a staircase, issuing one request at a time, one after the other. Each request taking 100-200ms even if the request itself returns only a couple of bytes.
The workstation has Symantec Endpoint Protection installed (12.1), and also Digital Guardian software (4.7).