When completing the federal tax return which is well before you even start the state tax return, under the Deductions & Credits tab there's a selection for Estimates & Other Taxes Paid. In that section you have sub-sections where you can enter taxes paid to the IRS, as well as taxes paid to one or more states. That's where you'll enter the $15K you paid to NJ, and it will be (should be) picked up by the NJ state return at some point when/after you start working on that state return.
