Very slow login to APM login page with Active directory creds

We have an APM Virtual server that has login page using active directory auth and gives webtop reosurces based on group membership. When user puts in cred and clicks login, it takes around 20-30 seconds for webtop to load. I'm wondering if its something to do with the active directory query taking ages, we do look for nested groups. Has anyone else had this issue? User experience is bad as it is so very slow. If anyone knows how to troubleshoot this or speed up the login that would be great. Thanks