Married/filing jointly has a 15% tax bracket all the way up to $75k, with another $20k in std deduction/exemptions. But if you and your wife earn more than $95k/year, and are in the 25% tax bracket, then tax-exempt bonds could make sense.
Vanguard Target Retirement 2040 holds ~13% bonds right now. If at age 40 you're planning to retire at age 65, do you already have 13% in bonds? The closer you get to retirement, the closer you want your bond allocation to look like a retiree's.
But where Vanguard Total Bond yields 2.5% (or 1.9% after tax, in the 25% tax bracket), you can get 2.1% after tax from a tax-exempt bond fund. It's also helpful if you start saving outside your retirement accounts. So if your bond allocation is below target, maybe you can use some or all of the $15,000 to buy a tax-exempt bond fund.
I see Vanguard has a "Vanguard New Jersey Long-Term Tax-Exempt Fund Investor Shares" with a yield of 3.2% and a duration of ~7 years. I'd consider that an "intermediate", not long-term bond fund. But if you buy into that fund, the interest is exempt from both Federal and State tax.