My calf is exactly 15 inches. should i get the small/medium or large/xl?

I would get a large/xl. I know the 15" are between the med and large but for those days that your calf might be a little swollen before you even put it on or through the day... I think for comfort purpose to allow that margin get the bigger size.

Do these come in a pair?

yes they come in a pair. I haven't had an issue with the ankle band being too tight. If you have an ankle or foot issue with swelling also order the ankle one with it that also comes in a pair. that will help prevent it.

I bought 3 pairs and cannot find "how to wash" them anywhere. What do you say?

Hello, that's a good question! NEWZILL emails every customer a PDF that shows how to care for our compression socks/sleeves. Basically, NEWZILL recommends hand washing with warm water and mild soap or detergent. NO chlorine bleach. NO fabric softener as this can break down the compression fibers. Warm water rinse. Hang or lay flat to air-dry. May dry in a dryer on low heat or delicate setting. However, if you prefer machine-wash, placing your stockings in a mesh laundry bag will help protect them during the wash cycle. Please contact us at CS@NEWZILL.COM if you have any further questions. Thank you!