No, don't report box 15 as NJ for both lines. You will have 2 separate line items for boxes 15 - 17. One will be NJ for Box 15, with the NJ wages as reported in box 16, and the NJ tax withheld from Box 17. The next line will be DE, with the DE wages from box 16, and the DE tax withheld from box 17.
You can't report NJ for both lines, because there was tax paid to Delaware, and box 15 determines how to report the tax paid on your state return(s).
