15. (15 points) In a certain year, there are 53 Fridays and 53 Saturdays. What day of the week was March 1st in that year?
【Analysis】 $365 \div 7=52 \cdots 1,366 \div 7=52 \cdots 2$, and a year has 53 Fridays and 53 Saturdays, indicating it is a leap year, so January 1st is a Friday. From January 1st to March 1st, there are $31+29=60$ days, $60 \div 7$ $=8 \cdots 4$, so March 1st of this year is a Tuesday. According to this, the answer can be derived.

【Solution】Solution: A year with 53 Fridays and 53 Saturdays indicates it is a leap year, so January 1st is a Friday:

From January 1st to March 1st, there are $31+29=60$ days
$$
60 \div 7=8 \cdots 4
$$

So March 1st of this year is a Tuesday.
Answer: So March 1st of this year is a Tuesday.