You may experience a slow navigation while you get access to Google or Google search results pages, this issue may come from a trojan that has been placed in the windows folder. For example syspol32.dll.
Install Avast if it is not yet installed on your computer and launch a deep scan of your hard drives.
It may also come from a script or a plugin on your browser, like Google FX.
Try also to disable query suggestions of your browser search engine in search settings.