Go to Bitcoin 0.8.5 Console Window and run :
dumpprivkey "myaddress"
Then in bitcoin 0.15.1
importprivkey "mykey"
if you don’t need to unlock your wallet even if it’s encrypted since you are using Bitcoin-qt not RPC commands and you’ve already set your password when you started it.
if you don’t want to use bitcoin-qt. go to terminal and run on v.8.5.0:
unlock your wallet if encrypted
(space)bitcoin-cli walletpassphrase "passphrase" timeout
Get private key of any address:
(space)bitcoin-cli dumpprivkey "myaddress"
if your wallet is encrypted run:
(space)bitcoin-cli walletpassphrase "passphrase" timeout
Then go to the latest version and run:
(space)bitcoin-cli importprivkey "mykey"
The space before the commands is important to the command will never be saved to logs.
