Ice bath in the kitchen sink is fine, just dont forget that you probably will be topping off so dont get it all the way down to the temp you want, but if ya do just warm up your topping off water a bit to compensate.
My kitchen sink will overflow from one side to the other so what I do is to build a little "dam" with a clean rag or towel (leaveing a gap for water to run out on one end) then put the ketel in the sink and fill the sink with cold water. I leave the water run very slowely and then add the ice. The reason I leave the water run is to flush out the warmer water and try to keep colder water in the sink moving. This may not work for you depending how warm your water is this time of year. My tap water is like 47f this time of year and jumps up to a chilly 56f in the summer, but then again it's sucked out of the bottom of Lake Michigan from like 5 miles out.
I can usually cool down 3.5 - 4 gallons in what seems like 20 minutes, I never really timed it.