Reduce queue time for SFMC API requests

Question

When using the Salesforce Marketing Cloud (SFMC) SOAP API, e.g. to run a Query Activity, we notice a task gets created. The task initially has a Status: Queued until Complete. This queue time can be significant. Also, it seems that when we repeat a certain call a few times (e.g. during testing), the queue time increases.

We are looking for a way to reduce this queue time. In the docs I found a bit about priority.

My questions:

1. Is this something that can be used for all SOAP calls? If so, how?
2. If not, is there another way?

Regarding point 1, it might be possible it's only relevant for triggered sends, since a Google search returns results where it is mostly described in such a context, like here.

Here I tried to use priority which resulted in an error:

<soapenv:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<PerformRequestMsg xmlns="http://exacttarget.com/wsdl/partnerAPI">
<Action>Start</Action>
<Definitions>
<ns1:Definition xmlns:ns1="http://exacttarget.com/wsdl/partnerAPI" xsi:type="ns1:QueryDefinition">
<ns1:PartnerKey xsi:nil="true"/>
<ns1:ModifiedDate xsi:nil="true"/>
<ns1:ObjectID>IDHIDDEN</ns1:ObjectID>
<ns1:Priority>High</ns1:Priority>
</ns1:Definition>
</Definitions>
</PerformRequestMsg>
</soapenv:Body>

Here I tried priority which did not seem to make a difference (the call worked as before):

<soapenv:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<PerformRequestMsg xmlns="http://exacttarget.com/wsdl/partnerAPI">
<Action>Start</Action>
<Priority>High</Priority>
<Definitions>
<ns1:Definition xmlns:ns1="http://exacttarget.com/wsdl/partnerAPI" xsi:type="ns1:QueryDefinition">
<ns1:PartnerKey xsi:nil="true"/>
<ns1:ModifiedDate xsi:nil="true"/>
<ns1:ObjectID>IDHIDDEN</ns1:ObjectID>
</ns1:Definition>
</Definitions>
</PerformRequestMsg>
</soapenv:Body>