OnePlus made a big deal of the camera in the OnePlus 2. There's a whole page on its website to brag about features like laser autofocus and optical image stabilization. However, some owners on the OnePlus forums have been raising concerns about whether or not the image stabilization is even enabled right now.
This concern was brought up when some OP2 early adopters noticed their shaky hands were not being countered by OIS as you'd expect. Interestingly, various system info apps report no optical image stabilization, but we decided to test it. Above you can see a video shot by the OnePlus 2, then a very similar video shot by the Galaxy S6. I'm shaking the phones roughly the same in each video (you'll have to take my word on that), and the OnePlus 2 video is much more shaky. Both were shot at 1080p and default settings (including video stabilization for the GS6).
So there are a few possibilities here. First, the OP2 does have optical image stabilization, but it's not very good and the system info apps aren't reading the settings correctly. Second, the lack of OIS could be a bug in the camera app and a future OTA will fix it. Lastly, OIS may have been left out on purpose and will be delivered in a future update. There may also be some additional digital stabilization that's isn't functional on the OnePlus 2. Whatever the reason, OnePlus should probably clarify things.