If you are hosting Deskpro On-Premise on Windows, you must edit the DP_DATABASE_HOST line config/config.database.php to be:
$DB_CONFIG['host'] = 'localhost';
The default value, 'localhost', will cause very slow performance.
You should have been prompted by the installation wizard to make this change, but if you restore the default config.database.php for any reason, remember to change it again.
Note that you should also use 127.0.0.1 as the domain for users in MySQL.