Lazy loading product loop - https://www.shopify.com/partners/blog/lazy-loading

lazyloading-products-loop.liquid

{% for product in collection.products %}
   {% include 'responsive-image' with
        image: product.featured_image,
        image_class: "image",
        wrapper_class: "image-wrapper",
        max_width: 700,
        max_height: 800 %}
{% endfor %}