It is possible to use a single data connection for several different QueryDB queries, but this makes form design considerably more challenging because
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The secondary data connection's data source will be based off the query you used when initially setting up the data connection.
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The contents of the data source will change every time it is requeried, which means you will need to copy the data somewhere else if you intend to use it for more than a very short period of time.
However, I doubt that going through all that is going to speed up your form much, if at all. It will make the XSN a little bit smaller, so the initial XSN download will be marginally faster, but if your form is slow from making a lot of queries, making a lot of queries through a single data connection is not going to change that.
Perhaps your form is performing queries that it does not have to perform when it initially opens? If there are some queries that only need to run after there is some user input, you can turn off the option to query those data connections when the form is initially opened, and that should speed up your form a bit