Taxes in FI = Is this right?

Assumptions:
Portfolio of $1.8mm. Withdraw 72K (4% of the portfolio)

Taxable gains Taxes
T-Notes: 18,000 2,346
(used federal tax table)
Stock div: 25,200 3,780 (15%)
Stock cap gain 28,800 4,320 (15%)
$72,000 $10,446

Average Tax Rate: 14.5%

Assumptions: I pay nothing but federal taxes (I tried searching the web to see if I was doing this right but I could not find the answer). I owe no state or local taxes on the Treasury note interest. I assume that I only need to pay the 15% tax rate on capital gains and stock dividends (no state + local taxes).

I understand that one can get into an even lower tax rate if their taxable income is under $30-something thousand, but am I right in thinking that the IRS counts capital gains, stock dividends, and T-bond interest as income?

Is there a way to lower my tax rate?

Any comments would be welcome.