iOS 9 downgrade

[baha2012]

I have ios9 on my iPhone 6 Plus,can I downgrade to 8.3 so I can jailbreak my device ?

 

[J. A.]

Welcome to iPhoneForums, baha2012!

Long explanation:
The only software versions you'll be able to install, are the ones signed by Apple. At this moment, these are 8.4.1, 9.0 and 9.0.1.
It's not possible to revert to another iOS. During the installation, your device connects to Apple's servers, to make sure you don't try to install different software versions than the ones signed by Apple.
Short answer: no, it's not possible to revert to 8.3, and it's also not possible to jailbreak the current versions.

Hope that helps.