Can you work on 2 different years at the same time and how? Not thinking about it, I upgraded my Mac OS system to run the current year but now I can't access 2015. help?

[DingnengW]

Yes, you can.  You will need to run two programs from each year at the same time.   However, if you have a printed copy of your 2015 return, it might work better if you just need to look up something particular.  If you need access to your 2015 return, see the following TurboTax support FAQ on accessing a copy of a 2015 or earlier return completed using the online editions -https://ttlc.intuit.com/questions/1900748-how-do-i-get-a-copy-of-a-return-i-filed-in-turbotax-online

Once the PDF has been downloaded to your computer, you can view or print the return with any PDF compatible viewer, such as Adobe Reader.

Getting TurboTax 2015 to work on the new Mac OS may be a challenge, but I was able to open TurboTax 2016 and 2017 on my Windows 10 laptop, followed with getting the updates, then able to view the corresponding year's tax returns.