Many systems that send HL7 over HTTP use very simple requests -- they just send the raw HTML as the HTTP request body. There's no SOAP layer on top. This is the approach that EnsLib.HL7.Operation.HTTPOperation uses.

HTTP docs say that 415 could indicate that the content-type header is specifying a content type that the receiving system doesn't like. Assuming the recipient doesn't actually need SOAP, if you can find out what content type they are looking for, you can change this in the Business Operation settings under Additional Settings/ContentType.

If the receiving system really does need a SOAP call you can look at EnsLib.HL7.Operation.SOAPOperation. I haven't seen this in use so I don't know the details but it might be worth a try.

Here's how you can iterate through the results:

 set query = "SELECT Facility FROM FROM osuwmc_EnterpriseDirDB.RelationshipMedCtrID WHERE OSUmedcenterID = ?"
 SET rset = ##class(%SQL.Statement).%New()
 SET qStatus = rset.%Prepare(query)
 SET rset = rset.%Execute($Get(ID))
 
 while (rset.%Next()) {
    // Check Facility value in each row
    set facility=rset.%Get("Facility")
    if (facility = "SOMEVALUE") {
        //...
    }
 }