Same here. I had a 5S that didn't have Siri issues and hadn't updated to 9.0.1 before trading in for a new 6S today. I didn't try Siri on the 6S before updating to 9.0.1 when I got home and restored from a backup and updating. But now Siri is silent. I switch her to another voice and it works fine like you said. Also going to wait it out because I'm not dealing with resetting all my settings.
Voiceover (which I hate and accidentally activate all the time) also doesn't work while you have your Siri voice set to the default female. If you change your Siri voice to, say, British English, but leave your Voiceover voice alone, then Voiceover will start working with the default voice again, too. Clearly a bug.