A legitimate android 64 bits build like 64PTB1115 should come with an MD5 or SHA256 checksum. Compare this after download.
(Word count: ~1,450)
If your device is running a pure 64-bit kernel and 64-bit user space, you are leaving behind the legacy 32-bit overhead. This is the baseline for the new 64PTB1115 build. android 64 bits bitly 64ptb1115 new