Before you blame Microsoft and Xbox team for slow download, check your internet connection and port forwarding. Everything is working absolutely fine for me after doing some work on my router. :
Slow Network Link speed (WiFi) | SNBForums
Merlin Server - Slow Response and Report Downloads
RT-AC68U] Bug in Firmware: Lan speed slowdown!! Reproducible + Video! | SNBForums
Skynet - Skynet and Network Speed Test slow-downs .. | Page 2 | SNBForums
Skynet - Skynet and Network Speed Test slow-downs .. | Page 2 | SNBForums