Optimizing the SvcUtil generated proxies for single use scenarios

We use SvcUtil generated proxy to talk to a SOAP Web Service, which has tenant specific URLs. E.g. we might need the proxy to call https://tenantA.api.service.com, https://tenantB.api.service.com, etc.

On top of that, we use the proxy in an AWS Lambda function.

In general, the proxy (ClientBase derived client) can take around 10-15s on the first time we call the API on a specific tenant. The subsequent call would take 1-2s. We are already using the XmlSerizliation library (without it, we've seen the first call take up to 30s).

In the Lambda function, when we create and execute a WS call, we are always paying the above overhead cost of initializing and not get the benefit for subsequent calls except for 1-2 more calls that the function may do.

We could be working with 1000s of tenants so, pre-initializing and holding on to those clients is not an option (more so, in a Lambda function).

How do we optimize for this scenario?

If we craft a SOAP envelope and call the API using a HttpClient, the op takes about 2-5s. However, serializing the proxy classes to SOAP hasn't worked out for us (raised a different question here, regarding that). Removing the first call overhead from the ClientBase derived client would be the best option, if that is possible.