My images don't work on mobile

I tried to reduce all the images of my website to the miminum in jpg. But in mobile version, it takes a lonkg time to download all the galleries. But then I tried with a differente website, with the same MB transfer size and it works perfectly. So, this make me thing that the problem is in the platform, not in the images sizes or quantity. Is it possible that Squarespace is offering a really bad server/hosting/etc?