I have an ecommerce website and have a product slider with 3 images.

Currently, I serve them at the native size when viewed on a desktop browser (374x374).

I would like to serve them using retina image quality (748px).

However how will this affect my ranking due to load time?

Does Google take into account image load times even though these are done asynchronously? Also as its a slider, its only the first image which needs to load. Do the other images contribute at all to the page load time?