Yea, Celia, you are right that 15 for ONE bag is way over the market price for Constitucion, but not if your clothes fit in two bags. I live fairly close by.
There is a place near me in Balvanera we used to go to and it is 8 pesos/bag. Let me count the reasons to live in cheaper neighborhoods! She is on Chile between Pasco and Rincon if you are in the area. Totally trustworthy and nice. I loved that lady...until we got our machine! If you live near the Facu de Medicina, I have a friend from Taiwan who has a lavadero at Boulogne Sur Mer at the corner of Viamonte I believe. They have never washed MY clothes, but he is one of the nicest people in real life I have ever met!! So I would totally trust him with my dirty laundry, so to speak! haha!
Still, the bags in every place are pretty small. They only fit a couple jeans maybe 3 shirts some underwear and socks, no more than a weeks worth of clothes if you reuse pants and not including towels. It´s not normal to charge more for sheets in my experience but any kind of heavier bed clothes like alcolchado-bed comforters or blankets and also heavy coats, they always have a different price for because they are harder on their machines. Still, even though they do all the laundry FOR me, it felt like a ripoff to pay more for laundry here than a US laundrymat per month. Plus, I would rather do my own clothes!