TT Online is only good for one return per account. Unless you set up a second account for him, your overwrote the first return that you prepared.
Use this TurboTax account recovery website to get a list of all the user ID's for an email address. Run the tool against any email addresses you may have used - https://myturbotax.intuit.com/account-recovery
If none of the user ID's received will access your 2015 account, then use the option shown in blue on the account recovery website, "I don't know my email address or user ID"