Upgrade from Bitcoin QT 0.8.5 to latest Bitcoin Core 0.15.X

I bought and transacted BTC in 2013/2014. I had a Bitcoin QT 0.8.5 wallet. I plugged it in and it updated correctly to the latest block. It correctly showed my BTC balance. I made a transaction without enough fees, which has sat unconfirmed for weeks now. I decided to upgrade to the latest Bitcoin Core wallet and so downloaded it, checked the Checksum, and then loaded it. I swapped out the wallet file with my backup of my original wallet. For some reason, it only shows about 1/1000th of my BTC holding. I have got the blockchain completely up to date. There are no other transactions showing, only those I have made. I have gone back to QT 0.8.5 and it still shows the correct balance when the blockchain updates. What am I doing wrong in the latest Core version?