Recommendations

Hosting:

Due to the way Magento is designed. It is highly recommended that users of Magento have their own server either VPS or fully Dedicated. I would be seriously surprised if any shared hosting service could handle the requirements for Magento over bloated way of doing things.

Only with access to your own server will you be able to get Magento to work fast enough so that customers will not leave because they're bored waiting. I highly recommend you make yourself familiar with this thread available at Magento forums:

Speed up Magento:

http://www.magentocommerce.com/boards/viewthread/36225/

http://www.gxjansen.com/101-ways-to-speed-up-your-magento-e-commerce-website

Even with your own server the import engine used by Magento will take 11 to 12 hours inputting 15K products and it will also just timeout or stop working at random times. If anyone finds a way to speed up Magento Import engine, please contact me so I can let other customers of STCtoMag know.