There is no such thing as a nondeductible traditional IRA, only basis in nondeductible contributions that applies to all your traditional IRAs in aggregate, including your rollover IRA. Any distribution from a traditional IRA is a mix of nontaxable and taxable amounts in the ratio that your basis for 2017 has to the total of all of your IRA year-end balances plus any regular IRA distributions that you made in 2017. The rollover of the $1.5M to an IRA has caused nearly the entire amount of your IRA distributions made in 2017 to be taxable. TurboTax is calculating correctly that something like 4% to 5% of your traditional IRA distributions is a nontaxable distribution of basis with the remaining 95% to 96% of the distributions being taxable. Whatever amount of basis has not been distributed remains in your traditional IRAs (in aggregate).
I'm sure that this is not the answer that you were hoping to hear, but it is what is required under the tax code. Rolling a large 401(k) balance into a traditional IRA when you have significant basis in nondeductible traditional IRA contributions and would like to make distributions that are largely nontaxable is not an uncommon mistake for people to make.
