Download pictures from shared albums (icloud/Iphone)

Hey guys.

I'm currently trying to download pictures in shared albums to my Iphone so that I can then copy them to my Nas via the Synology Photos app.

But it takes hours to download the pictures in the shared albums! I have about 380 pictures in one album that I am currently trying to download. but there are more shared albums to come.

is it normal that it takes so long? my internet connection is perfectly ok, 250 mbit/s

i could download the pictures via the icloud.com site and upload them via the synology app website. but then the sorting is no longer correct.

any tips on what i can do to speed up the download?