Sony launched Xperia Z3+ a few days back. It was just a minor upgrade of Xperia Z3 and Sony is expected to launch a new flagship in the Q2 of this year. That device is reportedly Sony Xperia Z5 and it will have lots of upgrades.
The two major upgrades to Xperia Z5 is the battery capacity and the processor. Sony Xperia Z3+ is plagued with a lot of overheating issues due to Snapdragon 810 processor. Sony will try to resolve this by using the Snapdragon 820 processor which will be launched by then. Xperia Z5 will have 4GB RAM.
Another upgrade is the battery capacity. Sony Xperia Z5 will feature a massive 4500 mAh battery which is a lot more than the 2930mAh found in Xperia Z3+.
In addition, Sony will use the latest Exmor RS IMX230-based CMOS sensor for Xperia Z5 which will permit 4K video recording. Another new thing is the Fingerprint sensor.
Sony will launch this device sometime in September and it will be available in the markets 15-20 days after its launch.