I am working on a new Magento 2 website. Everything is fine on our test server, but now that we want to move it to the main server, the checkout update scripts are too slow. It takes around 10 seconds to update the cart on every change (such as payment method, shipping method, etc). I have checked the Network tab in Chrome developer tools, the problem seems to be from huge TTFB of every request:
set-payment-information : 6.7s
updatePaymentMethodPost : 10+s
totals-information : 9s
Even "add to cart" process takes a long time too (5-6s).
The page load time is fine and it is under 3 seconds. Cache and Redis are enabled and It is in production mode. This might be caused by a server misconfiguration, but I can not find it out. Any help is higly apprecieated.