My Virtuemart joomla (Version 1.5.15) site after i activate sh404sef (ver 2.1.9.787), it slows lower the website significantly.

How do i fix this?

Look for following files:

administrator/components/com_sh404sef/custom.sef.php (unwritable) administrator/components/com_sh404sef/logs (unwritable)
administrator/components/com_sh404sef/security (unwritable)
components/com_sh404sef/cache (unwritable)

Switch on debug mode in global configuration and examine a webpage right in front-finish. See the number of db queries are performed.

Now switch on your SEF extension - and repeat.

See all individuals extra db queries?

On standard hosting that is shared the extra queries can place you over your hosts the limit on db queries. Optimising queries, adding additio al indexes for your db might help. More effective hosting is generally amore economical answer. Alternatively - stick to the built-in SEFwhich works fine when the website is structured brilliantly.

As mentioned by others - you're very susceptible to attack - I *think*anybody can request your password totally reset in your admin account. Also - later Joomla versions contained many performance upgrades, as will later components.