If like many others you are experiencing slowed download speeds for app and game downloads right now on Xbox Live, you're not alone, and it is being investigated.
Hey, guys! We're currently tracking this, but we need a few things from you to help us out.
First, give all of the steps on our Troubleshoot Slow Game or App Downloads on Xbox One page a try. If that doesn't help you out, please post back with your Region, your internet provider, and a screenshot of the advanced settings page for your network here: Settings > Network > Advanced. We'll be able to pass that information along to the appropriate people and work on getting this resolved. :)
From Microsoft's comment, it appears that the issue - although known - isn't one that's obvious enough to fix, as it looks like they need help tracking the origin of the problems. The issue also appears to not be limited to European users, as first thought from Reddit comments, but affecting those State side as well, with one user reporting:.
It's not just a Europe isolated issue. (Unless I'm really lost.) I've been watching Gears download at the bits and kilobits per second ranges for hours now, while every other feature of the console runs fine. Destiny, netflix, whatever. It's not in the internet connection of the console or my modem, it has to be in their server (probably the game file host area).
On the Xbox Live Status page, it's green across the board, except for an unrelated issue relating to the IGN app on the Xbox 360 where those users are "having to press “Retry” in order to launch the IGN application, or experiencing latency when playing content in the app,"
So far, Microsoft has also addressed the issue through their customer support app as well, but have asked for users to check back in "two to four hours" before they can give out a "formal release on the status." That was six hours ago, and it looks like it hasn't been formally acknowledged on the Status page yet.