Show theme and year for all exhibitions with ticket prices lower than 15.
SELECT theme ,  YEAR FROM exhibition WHERE ticket_price  <  15
SELECT theme ,  YEAR FROM exhibition WHERE ticket_price  <  15
[{'Theme': 'Santa Claus and Rudolph the Red-Nosed Reindeer', 'Year': 2006}, {'Theme': 'Summer', 'Year': 2009}]