It is 1.5k to 2.5k per calling. There is a new calling each day. There are 7 days in a week. 15x1,500=22,500 or 15x2,500=37,500 per day. 22,500x7=157,500 or 37,500x7=262,500 per week.
The gold earned is per calling not per set of calling. Since you can store up to 3 callings at a time you don't have to do all 15 characters each day. The start of the rotation will have you miss out on some callings by delaying some of the 15 characters. But if you work on 5 the first day, 5 the second, and 5 the third day you will be able to complete 3 callings on each of those sets. Instead of having to do 15 the first day, 15 the second day, and 15 the third day. You could do all 15 the first day and be done for 3 days as well. There are lots of ways to break it up so it isn't as burdensome as 15 characters doing 3 callings in one day.