We have developed an app based on swift 1.2 but we faced several bugs with iOS9.
Is it recommended to update to swift 2.0?
I am not a developer and I am getting different feedback from my developers - Yes it is needed no it is not etc
Is it recommended to update to swift 2.0 to support ios 9 on our app?
Depends on the bugs you faced.
If fixing any of them requires iOS 9 SDK, you have no choice. Migrate your app to iOS 9/Xcode 7/Swift 2.
If you can fix all bugs with iOS 8 SDK/Xcode 6, you have no need to rush into Swift 2. Though testing your app on iOS 9 devices or sims is not easy, maybe some of your developer have thoughts about it. Well-made apps built with Xcode 6 will be approved by Apple and run on iOS 9.
Generally, in production scale of an app, you need some amount of time to migrate it to Swift, which is far longer than `re-build it in a new Xcode, and fix a few parts marked as errors`.
We felt Swift 1.2 was not complete enough so we ported our 30 KLOC application to Swift 2. There are also major improvements in Xcode 7 for Swift so I suggest you should update to the Xcode 7 / Swift 2.
I wish Apple knew how hard I've been screwed by these "major improvements"...
Bear in mind if you are using any third party code/libraries, they will have to be Swift 2 compatible as well, as you cannot mix Swift 1.2 and 2 in the same project. So I would check those first.
I just completed upgrading a project from 1.2 to 2 and it was a bear, I had hundreds of errors and it took me the better part of a day to get it working again (even after Convert > To Latest Swift Syntax). But I'm glad I did it, now all my code is compatible again and I can use all the Swift 2 features like guard, try, etc. I think Swift 2 is going to be the last major project-breaking update for a while, probably until WWDC next year and even that will probably be more minor changes and additions.