I want to transfer my WhatsApp chats from my iPhone 6 with iOS 8.4 to my new Samsung Galaxy S6e, is there an easy way to do that?
As far as I am aware, as the iOS system has a built-in restriction that stops one accessing its filesystem, you cannot get access to the conversation history backup files.
Even if you managed to obtain read/write access through a jailbreak of some sort, the iOS messages dump might not even be of a compatible format to be displayed on Android.
In short, there is no easy/safe way to transfer your WhatsApp conversation history between iOS and Android. Android to Android, however, is a different matter.