Uploaded images size

It's probably because you configured an "image width/height" in the configuration of HikaShop in order to resize the images when uploaded and that you're uploading JPG files. HikaShop will resize them but with a quality of 100% in order to not degrade them.
Remove these configuration values and you won't have that problem when you upload new images.

Hi,

For the moment, there is no option to choose the compression quality.
But the new Image Helper functions introduced in HikaShop 2.1 have this feature. We would update our different views in order to use the new functions.

If you want to change the compression level, you have to edit the Image Helper (administrator/com_hikashop/helpers/image.php) and change the line:

$status = imagejpeg($thumb,null,100);