CREATE TABLE table_15915 ("School" TEXT, "Location" TEXT, "Founded" FLOAT, "Affiliation" TEXT, "Enrollment" FLOAT, "Team Nickname" TEXT, "Primary conference" TEXT)

How many of the schools are designated private/Presbyterian?
SELECT COUNT("Location") FROM table_15915 WHERE "Affiliation" = 'Private/Presbyterian'
SELECT COUNT("Location") FROM "table_15915" WHERE "Affiliation" = 'Private/Presbyterian'