Is there a way to move unmovable apps to the SD card in Android 6.0?
You just need a free app to do this without root. Please note that this does not work for preinstalled apps (like Google Play Books, etc.)

App: APK Editor 

https://play.google.com/store/apps/details?id=com.gmail.heagoo.apkeditor&amp;hl=en

Open the APK editor and choose 'Select APK from app'. Choose your app from the list that will appear and select 'Common Edit'. Change the 'Install Location' field to 'External Preferred'. Click Save and then Install. (you may have to uninstall it first.) You will now be able to use Settings/Apps or your preferred app manager to move the app to your SD Card.