there is a bug that is in IOS nine that prevents you from deleting the default siri voice that voiceover uses. I have found a work around, and while it's not as straight forward as it really needs to be, here it is.
1, go to settings, general, language and region and change your default region to something else.
2, once you do that, go in to settings, general, accessibility, voiceover, and speech. Find the default Siri voice and swipe up to delete. Double tap once voiceover says delete. there you go, done, it should be deleted from your device. After it is deleted, go back to language and region, and change your region back to yours. In my case, United States. And the default Siri voice that voiceover uses will be off your device. Keep in mind though, the default Siri voice that Siri uses will still be there. Hope this helps somebody.