If you reinstall, there are some precautions that you should take. Like, copying the salt key in config.php file, taking backup of userfiles and database and re-importing back.
Instead of this, I would suggest you to find the reason of site below slow.
Thanks PR, the hosting server was hacked, I have changed my passwords for the server access and FTP, there is malware on the site. The database as I can see has not been touched. The userfiles, is that the os_userfiles dir? I am thinking of just dumping the site and reinstalling then pointing to the database (keeping in mind the userfiles dir!) AND the salt file. Is this possible to restore the site to as it was before?