I just got married. Used TurboTax before to file individual return. Now will file joint return. Is transferring last year's return info practical or should I start over?

Did you both use Turbo Tax last year?

You can not transfer from or combine 2 returns or accounts.  Just pick the return for the spouse that has the most complicated return to enter or has any depreciation or business or  more investments.  Or use the account for whoever you want to be listed first going forward (by the way you can not change the order of the names).   Then add the other spouse's name, ssn and info to it.

You should usually  file a Joint return which is only 1 return combined for the both of you.  Make sure to stick with this one account for the future.  Just ignore the other spouse's account.

And info on Getting Married…..
http://turbotax.intuit.com/tax-tools/tax-tips/Family/Getting-Married/INF12006.html

Is it better to file Joint or Separately?
https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separately