Is there any way to transfer Whatsapp conversations from an Android 6 device to an iOS 9 device? I have already tried to use the software by iphone-to-pc unsuccessfully (could not read conversations from android device)
You can make a backup and upload it to Google Drive to restore it later with the other device.
I have no Apple device but I guess that synonymous there a backup from Google Drive can be restored.
One solution is to use WhatsApp Transfer, free software but only usable for three devices.
Make sure you have the latest version of Whatsapp on both devices and the last of iTunes on the pc.
On Android activate debug usb: Settings-> Device Info and clicks 7 times on Version Build.In the Settings menu there will be Developer Options where there will be the usb Debug Option.
Connect both devices to pc and open Whatsapp Transfer
On the Android you will appear to backup, you allow but without entering the password.
You will now have all your messages/conversations and in the left column the device you want to display.
Right-click on your Android device.
Click on the "transfer messages from android to iphone" and close Whatsapp on your iPhone.
Finally select the iPhone and click on confirm.