Should the distributions from inherited IRAs be included in line 7 of 2020 Form 8606 (and in line 11 of Form 5329 - year 2015-"Traditional IRA distributions included in income")?
No. This seems to suggest that you did not tell TurboTax that code 4 Form 1099-R indeed reports a distribution from an inherited IRA.
(Note the 2020 TurboTax currently has a bug where it is including distributions from an inherited IRA on the beneficiary's own Form 8606, but that bug does not appear to be present in 2015 TurboTax, at least not in the final version of 2015 TurboTax.)
