The reason to sell the car is not just to recover the current market value, but also to reduce insurance/registration costs (and if you're still using it, gas and maintenance.)
As everyone has gone over, the current market value is what it's worth. Now, the reason it didn't sell at $15k (or the price you have set now) could also just be "bad marketing." You need to get the target audience' eyeballs on your ad, and they have to like what they see. Lots and lots of photos that are as high quality as you're able to produce. List the unique selling points of the car.
When picking a price, sure you can (and should) consult KBB and Nada -- you should look at different condition levels and different price types (trade, private party and retail) to get a good overall picture. But you should also look at competitive listings -- you can expand the search area beyond what people will really shop if you can't find comparables, but there are a LOT of trucks for sale. Of course, north of the Mason-Dixon line, there are very few RWD trucks; not sure how D.C. is as it just misses the cut-off.
I'm interested in how you make out. I have a 2014 Silverado 4WD... that I hope to sell for ~$28k. Used trucks generally hold their value pretty well, but buyers are artificially biased against RWD, even though you get ~5 mpg better and 95% of the time or more, you get the same functionality you would've gotten from an equivalent 4WD.
Anyway, last year, I sold a car rather quickly and for more than what I expected. But I took excellent photos, so by the time the buyer arrived at my door, he was drooling and I didn't have to negotiate; his initial offer was excellent. That was using Craigslist only. Good luck!