I just bought a 1520 with WP8.1 Update 1 to replace my 1320 and immediately experienced this same phenomenon.
Of course, I recognized that the 1520 was always going to use up more power that the 1320 due to the combination of the bigger and faster quad core processor, double the RAM and the 1080p screen but I was shocked how much more quickly the 1520 ate up power compared to the 1320 and thought I was about to regret upgrading. The 1320 (with no battery saver until below 20% and brightness set on automatic) could last an hour and change while surfing the internet from 100% before it ticks 99% while the 1520 would eat up that much power in 20 minutes while on standby with everything switched off. And this is all with dark theme. For the first four days I was bewildered on how to solve this problem. I thought I probably bought a lemon with a busted battery.
I also didn't realize the capacitive buttons are permanently illuminated whenever you used the phone (even in daylight). The 1320's touch buttons by contrast are painted on. I think if there was some way to manually switch off the led lights or control the brightness for the buttons, battery life would be massively increased. Speaking of which, does anyone know how to do that on WP 8.1 Update 1? Right now, I've found a band-aid solution in the form of putting the phone on battery saver while keeping display brightness low (at 30%) or on automatic (30% brightness as well). With that setup, even if I was surfing the web, my power reserve nearly matched that of my old 1320 while at the same time my screen brightness/contrast is exactly where I want it to be: blacks are deep, whites are well-illuminated but subdued while the live tiles still look gorgeous. As far as performance was concerned, the 1520 doesn't take much of a hit with this setup. It's processing capabilities are so vast, even with battery saver on, it is still a powerhouse.
A more concerning development is that GT Racing 2 doesn't seem to download properly on the phone. Every time I've erased and reinstalled the app, the text and graphics are an undecipherable mess. What's with that? And why is CSR Racing not downloading ever since its update?