PP Team released its jailbreak tool 25PP compatible with iOS 8.4. We tested the jailbreak iOS 8.4 and no problems were encountered. However, you can perhaps wait for Cydia Substrate be updated because without it no tweak will work. It is possible that some packages are not supported by the Jailbreak iOS 8.4.
If you decided to jailbreak, you can found PP Jailbreak tool for iOS 8.4 to our jailbreak tools page, not currently supported for Mac – PPGhost use the Windows version and follow our tutorial.