Thanks for commenting. Yes, your cart/checkout pages are very slow (15-20 second load times). A few things stand out:

1. It looks like you are using generic shared hosting for your store. When using a host like this, MySQL is often not optimized, and usually the MySQL server is overloaded, or limited. Magento runs a lot of MySQL queries on cart/checkout pages, so in a non-optimized environment, it will be slow.

If moving to a Magento focused host that provides ample resources even in shared hosting is not an option, then your fixes are limited. But there are a few things you can try / check.

2. I see you’re running an older version of Magento (1.8). Try upgrading your store to the latest 1.9 version of Magento. This can help with speed.

3. Make sure your database is not bloated. Set log rotation in Magento to 1 day, so that MySQL tables like log_* are kept small.

4. Make sure PHP is at least version 5.4 and apply the php 5.4 patch to your Magento store. Make sure the php memory limit is high enough (at least 96 MB). If you can enable an opcode cache like APC or Zend OpCache, do so. This can help with cart speeds.

5. Consider implementing a CDN for images, js, and css files. It can help speed up overall page load speeds.

6. Look at implementing a Full Page Cache module such as Lesti or Extendware FPC. This will help catalog pages and searches run very fast once cached.

7. Make sure your Magento cache is set up properly. If you move to a more resource friendly hosting environment, you can load caches into memory using Redis, which can speed up page loads, even in the cart and checkout.

8. Try using a flat product and flat catalog setting in Magento and see if that helps with load times in the cart. This reduces the number of MySQL queries per page load.

My guess as to the major problem is that of your host. Using a generic shared host that is not a Magento expert and often loads thousands of accounts on each server does not suite Magento well. Migrating to a host that specializes in Magento will likely fix your issues.

You can check out our seamless Magento migration at:
https://www.lexiconn.com/ecommerce/magento/store-transfer.html

Hope this helps.

Rob