Fullscreen slider: stop image resizing plus image resolution down save problem

Hi there, I realised that no matter what image you upload, there is a script that resizes the image to 1500px width and downsaves the image again losing resolution.

see your example from the shop demo, it down saves this image:

http://kriesi.at/themes/enfold-shop/files/2015/03/fashion-girl-large.jpg

to this one: http://kriesi.at/themes/enfold-shop/files/2015/03/fashion-girl-large-1500×698.jpg

I want to use HD size images (1920px x 1200px) without the system further degrading the resolution. When I use an image at 1920px x 1200px, it is zoomed in to pixelization. When I upload a 1920px x 1200px full resolution jpeg (not saved for web), then the resized and downsaved 1500×938 image is too large in kb’s for my liking (at around 350kb’s)

Please advise how I can use 1920px x 1200px images where I can control how large in kb they are

Thanks in advance for urgent help