Ajax :: Sending Multiple Requests To Server

I need to send 15 requests to my server and get results, these results are queries to other sites. I then update my page with the results. I need to know if I am taking the correct approach, as things are working a bit slow, and i.e., seems the be as slow as a snail.

Here is my function for the first request
Code:
function one(){
var xmlHttpa=null;
try{
xmlHttpa=new XMLHttpRequest();
} catch (e){
try {
xmlHttpa=new ActiveXObject("Msxml2.XMLHTTP");
} catch (e){
try {
xmlHttpa=new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {
alert("Your browser does not support AJAX!");
return false;
}}}

xmlHttpa.onreadystatechange=function(){
if(xmlHttpa.readyState==4){
document.getElementById('resulta').innerHTML = xmlHttpa.responseText;
var el = document.getElementById('showMessagea');
el.parentNode.removeChild(el);
applystyle();
}}
xmlHttpa.open("GET","one.php",true);
xmlHttpa.send(null);
}

I then call this function and others from my page, one(); two(); etc. Am I correct in my approach?