There are actually many answers to this question. It seems that there are 13 digital answers, but the principle is the same, that is, the order of numbers is changed. It is easy to see this from the picture. I use a similar timetable to represent drawings, and I make them in the order from 1 to 15:

Combination1:23/45/67/89/10/1213/14157 group.

Combined with 2: 46/57/810/911214/13156.

Combined with 3: 47/56/81/9101215/13146.

Combination with 4: group 812/91310/4/154.

Combination with 5: 813/912/10/5/144 groups.

Combined with 6: 814/9151012/134.

Combined with group 7: 815/91410/3/124.

Draw a picture and it is easy to find that each number is used seven times.