There is only one file type that uses the .TT2015STATE extension:
TurboTax 2015 State Tax Form
A TT2015STATE file is a state tax form created by TurboTax 2015 tax preparation software. It contains one or more tax forms for a specific U.S. state and is linked to a .TAX2015 tax return document. TT2015STATE files may be referenced by TurboTax when completing a tax return.
When you begin filling out your state tax return, you will be prompted to download the tax forms for your specific state. You will click the "Download State" button, and choose your state. TurboTax will then download the TT2015STATE files for your state and automatically install them. After installation you can fill out your state return to finish your taxes. Since the TT2015STATE file is downloaded and installed automatically you will most likely never see the file.
TurboTax comes in Basic, Deluxe, Premier, and Home & Business editions. The Basic edition requires purchase of a TurboTax state return, whereas the Deluxe, Premier, and Home & Business editions come with one TurboTax state return included. You must purchase any additional state returns.
Updated: February 9, 2017