I was a Navy officer and rode two AAW cruisers for my first two ships as an officer. Carriers are incredibly fast. Their escorts, not so much! Carriers also have to turn into the wind to conduct flight ops which sometimes is 180 degrees out from the intended track. When they turn, most often the escorts do too! You calculates a 15 knot SOA, which is probably good most of the time, except in bad weather, heavy seas, or you you are not doing UNREPs to keep the escorts fueled. You also failed to account for other than a straight line course. Islands, shoals, and other ships often get in the way of where you are going.
If I got in my car and drove 700 miles from my home in TN, I could get to Florida. It would take me three days at that speed to make the west coast. The trip that battle group made was nearly 5000 nautical miles, so even using your calculations, it would take a week.
Now, consider yourself schooled in marine navigation.