If you used Online TurboTax for 2015, I can tell you how to find the other account. Whether you can view the return in it will depend on whether it was prepared in Free Edition or another edition. But we'll worry about that bridge when we get there.
To get a list of your User IDs and recover account access, you can use the tool at the link below. Try using your phone number first. If you try using your email address, and you have more than 1 email address, you should run the tool on each one.
NOTE: Before running the account recovery tool below, log out of all Intuit accounts including this user forum, or you might end up in a loop. Then clear your browser Internet cache, close your browser, then reopen it, and go to the link below. You may wish to copy this link so you can paste it into the new browser session.
https://myturbotax.intuit.com/account-recovery
If still no luck after running that on your phone number and each email address you have, then run the tool yet again, but this time choose the small blue link that says "Try something else", and it will look you up by SSN and other parameters.
