Currently, wbsearchentities always returns the full URL for each matched entity. Determining the URL is potentially expensive, and not always needed, so it should be optional (and perhaps off per default).
A parameter could be added to getAllowedParams, perhaps called props. Its default value would be an empty array, one possible value would be "url".
The URL is added to the result by $title->getFullUrl(). This should only be called if "url" is in the list of requested props.