The filesize of the images you uploaded don't have any impact on the page load.
When you upload your images, HikaShop resizes them automatically into thumbnails which have a small size (provided that the thumbnail size you setup is small, which is the case in your case). So whether you upload images of 50k, or 5Mb, in the end, they are all resized to thumbnails of 25k, and that's the thumbnails which are used everywhere. The full image is only displayed on the product page when you click on the image.
The fact that your website takes time to load sounds more like a problem with the number of resources you have on your pages and the time it takes to your server to send them to your browser. Tweaking the server settings to improve the speed and using tools to combine js and css together might help improving that, but you can't do much in HikaShop to help.