site loading slow / image specs

Site URL: https://www.movingportraits.nl/

Hi Experts

I’m helping my girlfriend with her new site www.movingportraits.nl

Unfortunately the images load terribly slow. She did upload PNG screenshots with most of her image content (without asking me beforehand 😉 )

Might the larger file size PNG be the cause of the images to load slowly?

if so, I find this very strange, because in the help docs Squarespace claims to automatically process the uploaded images to different file sizes (and I assume custom JPG?) settings to meet the perfect SQ standard...?!

Or DOES Squarespace keep the original (too large file size) PNG image file in tact...?!

Sorry to say, but the unclarity about how SQ is processing images in the background (or not processing them at all?) are quite frustrating. 

Who knows exactly how this works? And should we avoid PNG’s uploading in general, to speed up loading time?