Redirection Too Slow After Payment

When customer pays through any mode, the payment screen disappears (as usual after payment) and it should redirect back to woocommerce checkout page where it should display the message whether the payment is successful or not. Yes. It displays the right message. But the problem is that the redirection takes too much time (>40 seconds in my case). Technically it should be instant (<3 sec). Will you please help me resolve this issue asap?