I'm going to a music festival somewhere far away, and we're camping there for 4 days, I wanna know how long my iPhone 6 would last if I set it to Low Battery Mode the whole time?
Also what about the Apple Watch if its on Power Reserve mode?
Apple says about 3 hours more, whatever that means. If the optimisations to iOS 9 hold up, in total 4 hours more. However, we haven't seen anything more specific yet and I'm not sure whether Apple has disclosed in detail under which circumstances this was tested. If you're aiming for longevity, it's best to turn off all features that you won't be needing and keep the active usage (i.e. with screen on) to a minimum. You can get really good standby times like that.
In addition to LPM, based on its current state, consider turning off Wi-Fi and Bluetooth, potentially also LTE or 3G if you can. Turn off push notifications that you don't need, turn off (some) location services, reduce the brightness as far as you can. This should make sure that many background processes are not draining your battery even in standby and reduces the energy consumption while in active use. LPM is only a starting point, but it does offer things that can't be done elsewhere, like throttling the processor and networking.
Watch Power Reserve is said to last you 4 times as long as normal. If you can get through a day on your watch, it should be able to last you through the festival.
