CRM 2011 Upgrade to 2015 old SOAP

We did upgrade CRM 2011 to CRM 2015 and now we have a old SOAP that does not work in CRM 2015.

Could someone help me out with it?

Here is the code:

function GetProdText() { 
 
  var lookup = new Array();
  lookup = Xrm.Page.getAttribute("productid").getValue();
  var prodid = lookup[0].id;
  // alert(prodid);
 
   // Prepare the SOAP message.
   var authenticationHeader = GenerateAuthenticationHeader();

         var xml = "<?xml version='1.0' encoding='utf-8'?>" +
         "<soap:Envelope xmlns:soap='schemas.xmlsoap.org/.../envelope'" +
         " xmlns:xsi='www.w3.org/.../XMLSchema-instance'" +
         " xmlns:xsd='www.w3.org/.../XMLSchema'>" +
         authenticationHeader +
         "<soap:Body>" +
         "<Retrieve xmlns='schemas.microsoft.com/.../WebServices'>" +
         "<entityName>product</entityName>" +
         "<id>" + prodid + "</id>" +
         "<columnSet xmlns:q1='schemas.microsoft.com/.../Query' xsi:type='q1:ColumnSet'>" +
         "<q1:Attributes>" +
         "<q1:Attribute>description</q1:Attribute>" +   //add more fields that you want to fetch
         "</q1:Attributes>" +
         "</columnSet>" +
         "</Retrieve>" +
         "</soap:Body>" +
         "</soap:Envelope>";
         // Prepare the xmlHttpObject and send the request.
         var xHReq = new ActiveXObject("Msxml2.XMLHTTP");
         xHReq.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
         xHReq.setRequestHeader("SOAPAction", "schemas.microsoft.com/.../Retrieve");
         xHReq.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
         xHReq.setRequestHeader("Content-Length", xml.length);
         xHReq.send(xml);
         // Capture the result.
         var resultXml = xHReq.responseXML;
 
        // Check for errors.
         var errorCount = resultXml.selectNodes('//error').length;
         if (errorCount != 0)
         {
             var msg = resultXml.selectSingleNode('//description').nodeTypedValue;
             alert(msg);
         }
         // Display the retrieved value.
         else
         {

Xrm.Page.getAttribute("description").setValue(resultXml.selectSingleNode("//q1:description").nodeTypedValue);
         }
}

Maybe build a Rest or oData?

Thank you and best regards,

Dennis