unable to export products

I've never heard of such error, but I would say that it might be because you have too much data for the resources restrictions in place on your hosting.
Try to select some products and click on export instead of exporting all the products. That should use a lot less resources and give you the CSV file for these products without errors. In that case, you should ask your hosting company to increase the max_execution_timeout AND/OR the memory_limit options of your php (sometimes you can do that yourself by setting up your own php.ini but that depends on your hosting).

You can always keep the current version you have. As long as there is no security issue in HikaShop, you should be fine.

Otherwise, you can try to install it again after doing a backup and try to do a partial export as I explained in my previous message. That will tell you if it comes from a server limitation, in which case you can contact your hosting compnay in order to increase your limitations.
Otherwise, you could do the update and then, when you do an export, you can do a backup of your website and restore it on your computer in order to do the export there, that should avoid that problem.

The only thing we changed between 1.5.6 and 1.5.7 on the export of products is this:
The query to load the images of the products now load them in the same order as displayed in the product edition screen.
The export now loads the translations of the products (in a future version, the translations will also be in the exported CSV).

So if you don't use content translations, I don't see why it would eat more resources as the rest of the export is the exact same code.

Only the information of the image is load the image itself is not loaded. So the size is irrelevant.