It gives a good idea or screen on time...but not standby.
But android M sleep mode should increase that. You are correct, but keep in mind the battery life "should" go up after the update.
It gives an indication of SOT under a certain test circumstance that is likely not indicative of real world battery results.
I love my Xperia Z3 but I get maybe only 30-60 mins max more SOT over the course of day than my S6 Edge. So my Z3 generally is 4 hours to 4.5 hours SOT with its brightness on auto 95% of the time.
If I took that benchmark above as gospel or indicative as
what I should be getting - then I should be getting at least another 6.5 hours SOT !!!! Likewise my Nexus 6 has never managed to out do the iPhone 6 Plus battery wise, but according to that test it should be doing so ....
So yeah, I'm more than skeptical on that specific test to be indicative of real world results -
but what at least can be taken from that is that it thankfully the new devices appear to be at least in the same ballpark as the better performing handsets on battery. Which is good.