that is not correct. The list does not tell you your rating before the contest. You had 1745 after the contest and it was reduced to 1714, because codechef decided the newbie bonus was too big. These changes have nothing to do with the contest.
Your rating before the contest can be found in the file linked in this comment
Overall your elo-rating changes are:
1664 after Starters 47
1701 after July Lunchtime 2022
1745 after Starters 50
1714 after Newbie Bonus recalculation
I will give you the same list. You can get the same data from the 2 shared spreadsheets.
1702 after Starters 47
1793 after July Lunchtime 2022
1716 after Newbie Bonus recalculation
the reason you got a minus 15 is because the old rating was inflated for you. It tries to even out.
It is confusing to get minus 15 after a good contest but this is sadly how it is right now.