It is likely that TurboTax can simply export its forms to a PDF document, which is what tax2015 to pdf conversion typically refers to. This may either be done with a dedicated export PDF function, or via a virtual PDF printer accessible through the File ► Print function. This is mainly used for printing / sharing / publishing reasons.
Without TurboTax it will be very difficult, if not impossible to produce a PDF document from a .tax2015 file.Open TAX2015 file Open PDF file
A tax preparation software developed by Intuit
A popular tax preparation software