obviously you are using the zend framework for your application. zend also offers a free application stack including the zend framework, called 'zend server community edition'. the zend server includes a number of useful tools, one of them is the zend optimizer+.
the zend optimizer+ can be used to increase the overall performance of your application without any application changes. this does of course not directly address your performance problemes because of you database access, but it may make the performance issues acceptable because of the improved overall performance. using the optimizer and zend_cache as described in the other solution may be a viable way to solve your problem.