I'm a little disappointed. I don't really care about the specs of the phone but I do care about how it works for me and integrates into my life. So, in one example, I want a fast and smooth OS & app experience, but I don't care if it's running on the 16mhz CPU in my calculator or the 2.8Ghz i7 in my desktop.
What I do care about are features like these that offer some value in the way the phone fits into my life and my productivity with it. I use double tap to wake, I use glance, I use Cortana, I use flip to silence, I use things like Data Sense & Battery Saver. Those things feel like they provide value to me and allow me to interact with my phone in a different way that often feels more efficient. 'Hey Cortana' is another one of those features.
The 830 seems like it's almost my ideal phone but the lack of Hey Cortana is a little bit of a let down. I'd also prefer an AMOLED screen (even if that meant reducing the size by a 1/2" or so to keep the cost down). Neither of these things have turned me off the phone but they have moved it down from 'certain purchase' to 'I'll see how I feel in a couple of months'.
"Hey Cortana" is the one thing that has me still debating the 1520 vs the 830
Honestly if that is the only thing that's making you debate between the 830 and the 1520, then the 1520 is the one to get. Got one over a month ago and couldn't be any happier. Even though the 830 is the newer model, the 1520 blows it out of the water in practically every stat.