Spring WebFlux webclient async parallel calls

Question

I am new to WebFlux and learning and understanding the concepts.

I am just playing around with the parallel calls and merging them.

I want to make parallel calls (20-25 times) to one REST endpoint and consume the responses and make a list of responses out of it.

On an average each call takes arounds 2secs. So ideally if I am making 20 calls parallelly all these should be completed in 2 sec or max 5 sec if there is any call with high response. But in my case if I am making 20 calls parallelly it's taking around 15 sec but ideally all calls were below 3 sec. Could anyone please help me on what I am doing wrong here?

I need a blocking call here because once I get all the responses for these 20 calls I have to merge them and make a list of responses out of it.

Here is my web client:

public Mono<MyObject> getxxxx(String id) {
    Mono<MyObject> orderDetails = webClient.get()
            .uri(uri+"/{id}", id)
            .exchange()
            .flatMap(clientResponse -> clientResponse.bodyToMono(MyObject.class));
    return details;
}

My helper class from where I am calling my web client like for 20 times parallelly:

public Mono<List<Myobject>> listOfOrderMonos = Flux
            .fromIterable(ids)
            .parallel()
            .runOn(Schedulers.elastic())
            .flatMap(ids-> obj.getxxxx(ids))
            .ordered((u1, u2) -> u1.getDate().compareTo(u2.getDate())).collect(Collectors.toList());

From the above method I am getting list of my objects MONO.

After I get this I am using it by .block() method.

List<MyObject> response = listOfOrderMonos.block();

Thank you