How do I get my TurboTax returns that are older than 7 years? Specifically I’m looking for 2015 and 2016 which are no longer available online.

TurboTax and the IRS only keep tax returns for 7 years. After that you cannot get copies from either TurboTax or the IRS because they no longer have them, either online or offline. If you do not have your own copy, it is gone. There is no way to get a copy.