Q: is it a wise decision to install IOS9 beta verion on iphone

NO it is not, so don't do it and if you want to be a beta tester, then you need to sign up for this officially and you need to have 2 phones - one that you keep for daily use and the other as a tester, so you don't mess up your own phone.

You can't legitimately download iOS 9 without signing up for the beta testing, so if you do anything you do so at your own risk and get no help here.

I would not install it. If you are the developer you may test it. If you are the average user you may wait until the expected day of the release. Official release is expected in September so I guess it is better to wait.

Anyway if you will decide to instal Beta here is a good article: What to do before you install iOS beta - Apple Support