[Q] Installing Android M OTA manually on Android M preview

Currently my Nexus 5 is on Android M preview. I am trying to manually install OTA of Android M public release, but I get these errors on 50%:

failed to verify whole-file signature
signature verification failed Installation aborted

device details:
no root
no custom recovery
just bootloader unlocked
no changes in system files

Does manually installing Android M final release OTA work on device running on Android M preview? Or do I need to downgrade it to Lollipop first?

thanks!