Is it required to have Enterprise level developer program in order to do over-the-air installation, or can I do it using a normal developer program?
Over-The-Air IPA Installation Developer Program
You can do it with a regular developer account. With Xcode 7 they've resurrected the option to generate the plist when exporting for ad-hoc distribution. If you put the .ipa and the .plist on your web server with the appropriate HTML link (something like itms-services ://?action=download-manifest&url=https ://example.com/pat/to/myapp.plist) then you can install from the device. Of course the IPA has to be packaged using a provisioning profile that includes the devices on which you will be installing.
Caveat: I've been using this for years but I haven't been able to install this way on iOS 9 yet. I think it's just because I haven't upgraded my server with TLS 1.2, PFS etc. though.