I assume you are talking about the product listing page. The product listing page is programmed to only retrieve the products that are currently displayed on the page so it shouldnt be a performance issue related to the number of products in your database. That being said I do have a few questions about your install:
What other modules do you have loaded on the page?
Do you have any social networking buttons on the page that communicate with facebook, twitter, etc
How many products and categories do you have in your database?
Have you done any performance and tuning on your DNN site as outlined in the following post::
http://mitchelsellers.com/blogs/2009/...