No. The QDR II cannot operate below the lower frequency limit specified on the datasheet.
The QDR II has an internal DLL circuitry which is used to increase the data valid window and decrease the clock to output in the QDR devices. However, this DLL circuitry restricts the QDR II devices to operate at lower frequencies than the ones specified in the datasheet. So, if a user wants to operate the QDR II device at lower frequencies than specified on the datasheet, the user would have to turn the DLL OFF by connecting the DLL OFF pin to ground.
Please note that when the DLL is turned off, the device will have timings very similar to a standard QDR device.
For more information regarding the DLL off mode, please refer the attached application note on ?DLL Considerations in QDR II and DDR II?.