According to OnePlus, the OnePlus 2 will not receive an official Android 7.0 "Nougat" update. This means the OnePlus 2 will be stuck on Android 6.0.1 "Marshmallow". Forever.
OnePlus stated that their software development team initially didn't possess the knowledge it nowadays has. Why this fact still matters when releasing a new software update, is not known to the author.
While it was initially not known if the OnePlus 2 would still be receiving security updates, I have good news to report: The OnePlus 2 did receive a new security update in July 2017. This means that OnePlus is at least concerned about the security of their aging device.
Additionally, if you're an enthousiast, you can always install a custom version of the Android operating system on your device, such as LineageOS. Note that this software may contain more bugs and doesn't contain all the goodies of OxygenOS. It's up to you if that's worth it to get the latest Android version on your device...
Image credit: innovsoft.com.mx