If you don`t have a test device, you should definitely not upgrade to iOS 9 beta! Here are some of the reasons for which you should not:
Each time Apple releases a beta version for iOS, users are experiencing a lot of problems. Because that`s the beta for: fixing! So if you expect a full-working experience on iOS 9, forget about it! This is mainly for testing and helping out Apple engineers.
Yes! Upgrading to a new version of iOS for which there is no jailbreak yet, you will risk on losing it. Wait for an official iOS 9 jailbreak!
Remember Whatsapp on iOS 8? Until late September when Apple will release the GM beta version (which is basically the official iOS 9.0), there are low chances that developers release a compatible update.
Even if Apple warns you that you can`t downgrade from iOS 9 to lower versions, this is possible. But instead, you will not be able to restore a backup from iOS 9 on lower versions, because it`s not compatible. So as long as you want to keep your data safe, don`t update!
What are you going to do now? Would you upgrade to iOS 9?