Your question boils down to which tax break do you think the government will eliminate first:
- Long-term capital gain rate of 0% for those in the 10%-15% tax bracket
- The 15% tax bracket
My prediction would be the LTCG rate goes away first.
If you sell all your taxable securities first, I assume you will use some of the proceeds to fund your lifestyle over those three years. If you buy a $300k portfolio of dividend paying stocks with a 5% yield, you will have $15k of annual dividend income. At today's tax bracket, a married couple with no other income tax considerations can convert about $79,100 ($73,800 - $15k dividends + $12,400 standard deduction + $3950*2 exemptions) of your tIRA to a ROTH per year and remain in the 15% bracket.
I don't know how CA state taxes work, other than the perception that they are very high.