Dan Rayburn posted some information. collected by PeerApp and US ISPs on iOS9 download traffic:
".. around 1pm ET on Wednesday after iOS 9 was released, combined traffic from iOS 9 downloads spiked to almost 13Gbps. Nearly 80% (over 10Gbps) of this traffic is being delivered through PeerApp’s cache, avoiding congesting of the operator and University network.
Looking at individual systems, PeerApp said they are seeing speed improvements on the order to 10-20x; meaning customers served by their caches are getting the apple.com traffic 10-20x faster from cache. One University in particular is experiencing up to 100x speed improvement in downloads.
..In conversations I’ve had with some ISPs in the U.S., iOS 9 downloads have been accounting for anywhere between 8%-15% of traffic inside their network"
See "iOS 9 Download Traffic Peaks At 13Gbps Across 70 Telco & University Networks" - here.