ServiceKnownType causing WCF Service delayed connection

Question

I'm having a WCF service with wsHttpBinding. The service contract interface is declared with ServiceKnownTypeAttribute as:

[ServiceKnownType("GetKnownTypes", typeof(Helper))]
public interface IService1

The GetKnownTypes method returns a collection of 75 types.

I've tried connecting the service with ServiceKnownType and without ServiceKnownType.

It's causing around 2.3 minutes to connect with ServiceKnownTypeAttribute and less than 1 second without it.

If I don't use ServiceKnownTypeAttribute then I've to write minimum 3 APIs for each class i.e. around 225 APIs :(.. with ServiceKnownTypeAttribute the max APIs I've written are 10, which works excellent.

Can anybody suggest a solution?