For anybody still having this issue I finally fixed it after years of it being insanely slow. For the quest store on desktop you need to download a vpn, I think any will do including the free ones (I use NordVPN but I pay for that). Then vpn to a different location, I live in Japan so I VPN to Hong Kong, I don't know if that's the fastest but it's fast enough I'll figure it out with trial and error. My download speeds jumped up IMMEDIATELY, and I was downloading 1GB in a cpl mins or so.
Now, if you want to download to your quest 3 or 2 etc, you need to get a program called sidequest.
SideQuest (sidequestvr.com)
Choose the advanced installer, it's free.
Once you have sidequest connect your headset to your pc using a wire (just for the first time), and you can either connect it wirelessly after that or just use it wired whilst doing the following:
Once your quest is connected to sidequest go to whatever vpn you want to use, find the android version and download the 'APK', it should be there on the download page easily viewable perhaps in smaller writing somewhere near the download button.
Once the APK is downloaded for that vpn, simply go to sidequest, on the top right there's a button that says 'install APK from file', click that, click the APK in your download folder or wherever you put it, and it will install.
In oculus itself you won't see the vpn app, you have to go to your library and view untrusted sources, it will be in there, launch it, sign in, connect to whatever server you choose and watch your speeds jump dramatically.
This should all work without a problem BUT, there may be a problem so I'll cover it here just in case.
One thing a lot of people need to do to install any kind of APK on their device is to enable developer mode.
Here is a link to step by step instructions oon how to do that, it looks like it takes longer than it does trust me and it's well worth it because it means you can install all kinds of other good stuff:
How to Turn On Developer Mode/Debug Mode for the Quest 3 | by George Gorringe | SideQuestVR | Medium
After you've gone through these steps open up your quest on your phone app and go to the settings to make sure developer mode is turned on. Then sidequest should work perfectly and your vpn should also.
I hope this helps! I know this issue was murdering my brain for a long time.