It's asking for a employer ID number for box 15 but I'm from Washington state and this isn't applicable, right?

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

Use the Federal Identification Number (EIN) (Payer's ID) 

OR 

Make sure WA is not listed in Box 15