Then, you need to flash it on the device and get rid of all the
vendor_boot/dtbo mess:
fastboot flash boot boot.img-sony-xperia-pdx215
fastboot erase vendor_boot
fastboot flash dtbo emptydtbo.img
fastboot reboot
Where emptydtbo.img is a tiny file that consists of 2 bytes (all zeroes), doing
a "fastboot erase" won't cut it, the bootloader will go crazy and things will
fall apart when it tries to overlay random bytes from an empty partition onto a
perfectly good appended DTB.