Squarespace hopeless to open a gallery/slideshow on mobile

Site URL: https://soulfulreflection.co.uk/extended-portfolio

Why is squarespace so terrible handling images? 
I was on a competitor before, it would resize any image really fast and load really fast. 

On square space, if i have a couple of slideshows with 100 images that were uploaded at 1000px wide ( + Jpg mini'ed)  while the page loads fast on desktop, on a highend mobile phone, the images take 15+ minutes to load. 

Also most squarespace pages score 10/100 or less on google page speed test.

Any way of making images load faster on mobile? even if kill the resolution further on a specific page? It's killing me SEO and clients cant see their galleries.