The Marshmellow update is definitely causing many phones to turn on wireless transmitters, and leaving them on. For me it's cell signal and WiFi. If I used Bluetooth I would not be surprised if that was on for me too. What's odd is that there does not appear to be any particular app that's using any of these wireless links. I don't see unusual data usage. I just see the antennas turned on, transmitting who knows what to who knows where.
Turn ON airplane mode and monitor the phone for an hour or so; you should see battery usage go back to normal. Airplane mode shuts down all wireless... Bluetooth, NFC, WiFi, Cell Signal, etc. Turn airplane mode OFF and the antennas turn back on. WHY??