I haven’t published my site yet. It’s under testing. I have already optimized the images I use. The important point is this: I am using a high resolution image of the product. For example 1000 x 1000 px. The products listing on the store page uses the full size of this image ( 1000×1000 px ). However, it is more appropriate to use thumbnails. For example, let’s look at your own demo address:
https://burgerthemes.com/demo/lite/storebiz/shop/
Here the full size of the image is used:
https://burgerthemes.com/demo/lite/storebiz/wp-content/uploads/2021/08/image-8.png
It should be a thumbnail instead:
https://burgerthemes.com/demo/lite/storebiz/wp-content/uploads/2021/08/image-8-300x300.png