Thousands of people wore rainbow suits, held colorful flags and danced through the streets Sunday in downtown Oakland to celebrate the annual Pride Festival on its 15th anniversary.   Sunday’s festivities kicked off with a parade down Broadway, near 21st Street, to Frank Ogawa Plaza, where a ticketed event featured DJs, live performances and speeches from drag queens and politicians.  The festival included more than 100 booths by vendors and organizations, such as sponsors Gilead, a HIV-focused biotechnology company, tequila brand Patrón,…