That's a tough question to answer. There have been a few postings regarding even worse battery life after nougat. But I suspect that's a small fraction of most users. Overall, nougat has a far better doze function which in my case definitely helps my battery life. As far as your phone is concerned, have you tried the following steps, in order: –
1. Clear system cache.
2. Hard reset – kind of drastic but might be a better choice battery life is really bad.
3. Upgrade to nougat. You never really know, but that might, and I stress might, do the trick.
If none of these steps work, you clearly have a sub par battery and it's an hardware issue. Not sure about your warranty status, but I would take it back the original source