The answer depends on what you mean by slow.
If you refer to the initial loading time for a site, that is a "keep alive" issue. Refer to
this thread for more information. This is a characteristic of all ASP.NET websites.
If the issue is performance, then you might want to take a look
here for some suggestions. In my experience, caching seems to be the #1 issue. Unused modules and authentication providers can be another. And, remember to keep your database's log files clean.
Also, remember that performance is dependent on the server and database server that you use. If you are in a shared hosting environment, you might want to look at dedicated hosting, for example.