Looking at the transactions provided, it appears that the OP is saying:
He controls addresses:
- 1HesuRU5FUfxouHUd2zWXf3MqeVLzT7D8e
- 1Fg7taQf2yAwZqzdbBBAXz1gQnLaaMjsSu
At 02:18:57 UTC on 2017-03-12 he sent
500 BTC that were previously received at those three addresses to 17dQuN1NmUkvzq49haVw5CNC1SSKZx3PUb with transaction b3eae4e1be3ea7ee092d0f1dbf41a66d7409405699a99767e0deb813d1335fca with 0.08165803 BTC of change being sent back into his wallet at 1AHBpVk1GzkkTWNZnbMmWZg55uCEmvVamu
Then three hours later, at 05:27:06 UTC on 2017-03-12 the change from that transaction plus enough additional bitcoins that were previously received at 1HesuRU5FUfxouHUd2zWXf3MqeVLzT7D8e to add up to
ANOTHER 500 BTC were sent to 1CiRdpDsqsgxGz6Dv1kesaqsvkCp92cKWy with transaction 115e0cf22712d8c5b3dae7450b616207a5709c045a5d4ddcfa155cdb5b6d37b with 0.07192452 BTC of change being sent
back into his wallet at 1NhAojGKKVLcBSdm5vbxxddQSqCT695FsA.
OP says he sent the first transaction, but not the second one. But it that is true, then why did the thief only take 500 BTC and not the entire available balance (the wallet had an additional 983.95 BTC)? And why did the thief send any change back into the wallet?
Maybe they were hoping to hide the transaction in the wallet. Or maybe the OP accidently hit a few extra buttons on his keyboard and sent a second transaction himself.
It's difficult to imagine that the OP would send a 500 BTC transaction and not remember sending it, but it's equally difficult to imagine that a thief would only take one third of the bitcoins that they could take.
It is also odd that the OP couldn't remember that he sent 500 BTC (his original post claims that it was 100 BTC). There's a lot of things in this story that just don't make sense.
Yes, it is definitely unlikely that OP wouldn't remember it was 500 btc and also not remember sending the second tansaction. Those two look like there's definitely some links.
Also, OP, it's not considered good practice to store 1500
BTC in a bitcoin wallet that is connected to the internet due to the hacking vulnerabilities of such wallet (maybe try paper wallets or hardware wallets to store that amount)?