High Latencies In Socket.IO

I'm developing a game using Socket.IO . I'm finding that the latencies are very high ie 250 milliseconds even when running on localhost. Is this normal ?

Here is the code I'm using to calculate the latency :

function startLatencyPoller(socket,callback)
  {
      setInterval(function() {
      var startTime = Date.now();
      socket.emit('ping');
      socket.on('pong', function() {
        latency = (Date.now() - startTime) /2; //round trip time / 2
        callback(latency);
  });
}, 2000);

}

My question is whether its normal for Socket.IO to have latencies as high as 250 ms even on a local network and whether there are ways to reduce it further.

EDIT: I checked the transport and right now I'm using websocket as the transport.

EDIT: Problem has been fixed after editing code as per below answer (remove listener avoid them piling up) :

setInterval(function() {

     var startTime = 0;
     var socketFunction = function() {
        latency = (Date.now() - startTime) /2; //round trip time / 2
        callback(latency);
        socket.removeListener('pong',socketFunction);
    };

    socket.on('pong', socketFunction);
    startTime = Date.now(); 
    socket.emit('ping');


}, 5000);