I work in the state of Tennessee and on my W2 box 15 is blank. in the turbo tax system, it shows an error for box 15 and won't let me continue.

Several  states do not have a state income tax.  So these states will not show up in certain drop down lists.   Leave boxes 15, 16, and 17 blank when you enter a W-2 for these states.

Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington and Wyoming