The Sony Xperia Z2 features a number of improvements over the Xperia Z1. On the camera side this mainly focuses on 4K video and Timeshift video (slow-motion recording). However, the actual CMOS in both handsets is the same 1/2.3-inch 20.7MP Exmor RS chip. Both handsets also feature Sony’s G Lens and BIONZ image processing software.
You would therefore expect pictures between both handsets to be fairly similar, although this doesn’t seem to be the case judging by these comparison pics. They show an Xperia Z1 on 14.2.A.1.136 Android 4.3 Jelly Bean firmware against a Xperia Z2 with 17.1.A.0.417 Android 4.4.2 KitKat firmware.
The pictures were taken at the Xperia Z2 launch event in Jakarta. Judging by the crops below, it does look like the Xperia Z2 exhibits less noise than the Xperia Z1. Given that the Xperia Z2 firmware is only likely to get better before release, we could end up seeing even more improvements on launch.