When updating my package index, e.g. over
apt update it always has to download some very large entries, usually 20 – 40 MB with a Contents-* prefix. This slows down the update process very much also due to the reason that it seems like these packages are fetched multiple times. Usually they are named something like Contents-i386 or Contents-amd64.
I'm absolutely not sure if this is normal, but I'm a Ubuntu user for quiet some years and can't remember, that index updates where that heavy in the past. The problem could be related to some configuration change I had to made in the past but I can't really remember what it was.