It might be related to loading the images, as loading the images does require querying the database.
I think you have 2 options:
1. You can choose to display images without their URL being masked by using [product.image direct='1' tag='1']
instead of [product.image tag='1']
in your store's views.
2. Or you could choose to store the images locally which will result in an initial load on your server while each image is downloaded from the merchant's site and saved to your server but will result in much faster loading images in the future.
Here's more info: