Yes - Sandbox has been VERY slow.
Non-Production environments are not as responsive as production.
You may also be initially slow after a refresh because you have to recache all your regular pages.
Per experience, Sandbox is really slow after refreshing. Same comment with CDuf but if the poor performance continues for an unacceptable time, you may want to report it to NetSuite. They may have a way of getting it back to its normal speed before the refresh.