Let's have a look at this address on Etherscan: https://etherscan.io/address/0xfbe0aFcd7658BA86be41922059dD879C192D4c73 First transaction is a Smart Contract creation, that costs about 15 ETH. Can't understand where such address has this balance.
Actually the smart contract creation didn't cost 15 ETH but 15 ETH was passed to the smart contract as value. So the smart contract contained 15 ETH when it was created.
But for the actual question, it was rewarded from maining. You can see it at https://etherscan.io/address/0xfbe0afcd7658ba86be41922059dd879c192d4c73#mine .
In Ethereum there are two accounts, one is wallet account used by user to send and receive ether and to create smart contract, Another one is contract account.
For every payable transaction the ether stores in contract account. "payable" is the keyword in solidity. The functions in which payable is mentioned/defined user has to pay ether to call that function, this function known as payable function.
So in that contract, constructor is payable and user sent 15eth while calling the constructor and it stored in contract account. The 15 eth is deducted from user wallet account.