You can try this, see if it works for you.
Rather than choosing date from date picker, you can enable the date box using javascript & enter the required date, this would avoid excessive time required to traverse through all date elements till you reach one you require to select.
Code for from date
((JavascriptExecutor)driver).executeScript ("document.getElementById('fromDate').removeAttribute('readonly',0);"); // Enables the from date box
WebElement fromDateBox= driver.findElement(By.id("fromDate"));
fromDateBox.clear();
fromDateBox.sendKeys("8-Dec-2014"); //Enter date in required format
Code for to date
((JavascriptExecutor)driver).executeScript ("document.getElementById('toDate').removeAttribute('readonly',0);"); // Enables the from date box
WebElement toDateBox= driver.findElement(By.id("toDate"));
toDateBox.clear();
toDateBox.sendKeys("15-Dec-2014"); //Enter date in required format