It just depends on your Internet like before I had some crapy as wifi and it took like 3 hours to download the map pack and know I upgrade my Internet and now it only take 5mins to download
It depends on
1. Your internet speed
2. The amount of people using the internet
3. NAT Type
For #1, My map packs usually take around 10 - 20 minutes at around 2-3 Megabytes per second, check your internet speed, you may need to upgrade.
For #2, I'm usually the only one in my family using the internet which let's me take advantage of all the speed.
For #3, there are 3 NAT Types, 1 being the best and 3 being the worst, if you are on a wireless connection NAT Type 2 is the best your gonna get, which is what I have, and it's enough whereas if you have NAT Type 3, there is clearly a problem which involves your router