I have a 6S, and I have not felt too much difference in battery life... yet. Then again, I just got mine replaced with through the 6S battery replacement program, so maybe that's why.
my 6s plus was horrific, it has taken about 5 days for it to calm down, thats installing from IPSW set up as new. now it "seems" to be back to a reasonable state, i am guessing its the spotlight indexing going on.