These figures are skewed and will always be skewed. People have to adopt early if only to give them a chance of being able to downgrade if it all goes pear shaped. After that you have no choice anyway and iOS9 then ‘looks’ to be really popular.After the slightly bumpy iOS 8 release, this is surprising.
Edit: oh yeah... /s
That’s what I’ve done.
Back up to iOS8 first and make a copy of that ipsw, (incase the OS deletes it).
Upgrade to iOS9 immediately and have a good look around the OS.
If it breaks something you rely on or you just don’t like it, revert to iOS8.