So I should get sun at least 15 minutes a day
You should get at least 15 minutes a day, and in winter and north of the latitude of Philadelphia, even more. Also if you are dark skinned. In fact the difficulty of dark skin allowing Vitamin D formed in the skin to move into the body is probably the reason about 2.5 times more people with dark skin have been dying of Covid. One study of black men hospitalized with Covid found that 80% were very deficient in Vitamin D. Why doesn’t the CDC or other appropriate agency warn people of color they need more Vitamin D than light skinned people, or are they indifferent to letting Negroes and American Indians die in larger numbers?