Section 15.  A person holding an office by election shall continue to exercise his powers and duties until his office is abolished, his successor takes office or the office is vacated, as provided by law.  A person holding an office by appointment shall continue to exercise his powers and duties until his office is abolished, his term ends, or he is removed or replaced under the provisions of this constitution or by law.  Each public body shall continue to exercise its powers and duties until changed as provided by this constitution or by law.