I have a site to site VPN configured, when users access the Internet the response time is acceptable. When they access the main site's server resources the site drags. If they try to open up folders it takes a minute or two between each subsequent folder. On the main site, it is fine. I added a Host entry in the host table to determine if it was DNS, but that did not make any difference. This has been a chronic issue for months, and they are extremly frustrated.
I have this problem too.