I just installed apt cacher ng for catching my apt upgrade packages and saw a huge time improvement even though I have a good internet connection. It act as a proxy and caches the response packages.
Do you run something similar? Or maybe even run a local repo mirror? Warning, they are really big so I don't think it is recommended unless you really need almost everything.
I use apt cacher ng. Most of my use case though is for caching of packages related to Docker image builds as I build up to 200+ images daily. In reality, I have aggressive image caching so I don’t actually build anywhere close to that many each day but the stats are impressive. 8.1 GB of data fetched from the internet but 108 GB served from the acng instance as it shows in the stats page of recent history.