I keep hearing this creeking/squeeking, which seems to be coming from the passenger side rear wheel, whenever my car comes to a stop at 15-20 MPH and it

 

(as per your PM)
---- Some possibilities:
Have you ever had your hub nut checked for torque? Some have been reported as being loose and with the age of your car, this might be the case.
It could be wheel bearing noise. Sometimes, a wheel bearing won't make noise till it is heated up a bit and turning at a specific speed. Yours may not do it when cold and only do it when at low speeds. Next time you go for a good drive of about an hour or so at highway speeds, trying NOT to use your brakes too heavily or too long, coast to the side of the road and cautiously feel the center part of the wheel on both sides. If the bearing is going, the heat generated can infiltrate the wheel and one should feel much hotter than the other side.
Have you run into a curb lately? (Bent suspension?)
Or have you driven over an object that may have pushed on your ABS wheel components?
You can also try to put the back end of the car up onto jack stands and turn the wheels by hand and listen. A low speed squeek might be heard under these conditions when all is quiet.
Check to see if you have any loose wheel weights.
How's your ebrake travel? When you make this noise, try gently pulling up on the ebrake and see if the noise changes.
(OK, I'm tapped out.)