Hi Pooja,
When you increase the data rate you also increase the bandwidth of the conversion. Another thing to consider is the digital filter for the ADS1247 is FIR and the response changes with data rate. Look at the filter responses starting on page 27 of the datasheet. One thing that is often overlooked is aliasing. High frequency content can fold back into the pass band. This requires some sort of anti-aliasing filter on the input to the ADC. Usually all that is needed is a single pole RC filter. Do you have any filtering on the inputs of the ADS1247?
Best regards,
Bob B