I am sticking to last official Naugat update. More because I am hesitant to moding. Once I tried installing custom ROM on one of my phones and I was successful in bricking it

Fortunately it was cheaper phone. But definitely, I don't want to brick my Nexus 6.
Lately, I was struggling with battery life and frequent hanging of my phone. I had a lot lot lot of apps installed. So I factory resetted my phone and started installing only needed apps. At first it was good fast, but as installed more apps, it started to hang more and battery life is getting bad. So I started to think if custom ROM is the only answer. But, then I experimented with it. Trying to find how I can reduce hanging of my phone and extend battery life. And finally I have come up with awesome way to do just that. I follow these points:
- I always keep mobile in power saver mode. This saves a lot of battery. This also reduces performance a bit, but next point helps for that.
- I frequently (mostly before locking my phone) go to Settings > Developer Mode > Running Services and stop the running services which you don't intend to. Mostly this involves closing ES Explorer and ShareIt services among others. You may find multiple services run by each app. And also it takes time for services to stop. Many times I have to hit Stop button multiple times.
With this, my phone has become surprisingly snappier and also battery life is extended to more than one and half day. Nowadays, I charge it only once in the morning and battery is reduced from 100% to 50-60%.
Also, to note, I don't play games and watch movies on mobile. Most usage involve reading, browsing and music.
If custom ROM can increase the battery life, then definitely there is something wrong with official ROM. I believe Android is not really that great at app optimization. Or more correctly, allowing a lot of apps run in the background is the need of Mobile Phone experience. But, if you check in Settings > Developer options > Running Services, you will find a lot of unnecessary services belonging to unnecessary apps are running. That window also shows time for which the services running. Simply killing services running for longest period increases battery life and improves performance. For me ShareIt, ES Explorer are the ones (these apps are adding more functionality like crapware and running lots of services). And there were others too. Kill them.
Happy optimizing!!!