Change DPI from linked image

Hello ! I have made a script (see here) which batch center and resizes JPEG pictures, then save them as SVG.

The problem I have is that the SVG size is too big (5 MB instead of max. 200 kB). How could I lower the DPI of the linked pictures ?

I have noticed something: when I open the SVG and click on the linked picture in Illustrator, its size is 800x600 px (actually 900x600 but the artboard cuts the 100px more), but when I click on the linked image properties, it still shows the original JPG size (5472x3648 px). How come is that ?

Thanks a lot in advance for your help !