Sony has announced the availability of Android M Developer Preview images for several of its Xperia devices. Keep in mind that these are categorized as AOSP images, which means you won't be have the Google apps and services by default.
The list of eligible devices includes the Xperia Z3, Xperia Z3 Compact, Xperia Z2, Xperia Z1, Xperia Z Ultra, Xperia Z, Xperia ZL, Xperia E3, Xperia M2, Xperia T2 Ultra, Xperia T3, Xperia L, and Xperia S smartphones along with the Xperia Z3 Tablet Compact, Xperia Z2 Tablet, and Xperia Tablet Z tablets. These devices are all listed as part of Sony's Open Device Program, allowing anyone interested in developing apps for these devices to take them on. Unfortunately, newer devices like the Sony Xperia Z3+, Xperia Z4 and Xperia Z4v are not part of this lineup.
Sony warns that "AOSP software is not certified or intended for regular use", and that "the modem and the camera are not implemented", which means you shouldn't rely on Android M as your daily driver for the time being. However, if you are an experienced developer who has one of the above mentioned Xperia devices lying around, feel free to visit the source link below to get started.
source - Sony