I am having the same issue on my new 6S Plus. Over the last week or so Siri is worthless. She hears my commands, but can't handle any of them. She will eventually time out and ask me to try again. I reboot and I will get maybe one or two commmands before it goes tits up again.
Exact same issue here. Also 6s plus. I also have this issue on my iPad Air. I've tried turning Siri off/on, restarting phone, doing hard reset, and resetting network settings. Gotta have something to do with this version of iOS and certain devices if it's only affecting a few.