How to decrease the delay of the first request to a stunnel server

Question

When hosting an HTTPs bridge server using Stunnel to my HTTP server, the first HTTPs call takes around 15 sec.

After that, all subsequent requests take around 200ms which is reasonable.

But the first call is very slow.

According to the Stunnel FAQ, there is a way to improve the speed by turning TCP NODELAY on.

My connections are slow, slow, slow

One option might be to turn on the TCP NODELAY option on both ends. On the server, include the following options:

socket = l:TCP_NODELAY=1

and on the client include:

socket = r:TCP_NODELAY=1

Do you know another way to reduce that long delay because it did't help?