Socket.io performance on server is terrible

I'm using socket.io with express to create a real-time browser game for fun. Until today I tested site on localhost but I decided to test it on server, and it is so slow.

What I'm doing with socket.io on client is simple:

When a user press send button, I'm sending some datas:

socket.emit('details', {
                                user_id: .. , 
                                balance : ..,
                                amount : .. , 
                                payout : .. ,  
                                chance : .. ,
                                other : ..
                            });

On server.js

socket.on('details', function(data) {
    users.findById(data.user_id, function (err, docs) { 
        if(docs.length!=0){
            var user_id = docs.local.user_id,
            user_name = docs.local.email,
            clientSeed = docs.local.client_seed,
            serverSeed =  docs.local.server_seed,
            balance = docs.local.btc_balance,
            hash = someHash,
            user_id =  docs.local.user_id,
            user_name =  docs.local.email,
            id = (new Date).getTime(),
            lucky_number = /// CalculateRolledNumber();
            chance = data.chance,
            amount = data.amount,
            payout = data.payout,
            other =  data.other;
            CalculateGAME (amount, payout, hash, ..... , ..... ); // calculating

            }

        });

In CalculateGAME(...) function I'm saving some datas to MongoDB and returning some of them like this:

if (err) return handleError(err);
                     SOCKET.broadcast.emit('details_RETURN', { // to everybody
                        id : id,
                        amount : amount,
                        payout : payout,
                        betProfit : betProfit,
                        result : result,
                        _user : user_name,
                        chance : chance, //
                        lucky_number : lucky_number, //
                        seed : seed,
                        hash : hash
                     });

                      SOCKET.emit('details_RETURN___self', { // to me
                        id : id,
                        amount : amount,
                        payout : payout,
                        betProfit : betProfit,
                        result : result,
                        _user : user_name,
                        chance : chance, //
                        lucky_number : lucky_number, //
                        seed : seed,
                        hash : hash
                     }); 

And then get back it on client :

socket.on('details_RETURN', function(data) { 
         //AppendDatasToTable()

        });
        socket.on('details_RETURN___self', function(data) { 
        //AppendDatasToTable()

        });

As a result I'm doing:

• -Send data on browser
• --Get data on server.js
• ---Find user id on mongodb
• ----Get datas of user
• -----Calcutulate Sha512 of seed
• ------Calculate lucky number based on seed+id+other data using HmacSHA512
• -------Save game datas to mongodb
• --------Send some datas back to client(browser) with socket.emit and socket.broadcast.emit

Everything is good on localhost but on server, even mouse is freezing? Server details are: 4GB RAM, 60GB SSD, Ubuntu 14.04 (DigitalOcean).

How can I optimize my product? (I'm new to nodejs/socket):

Edit: I changed socket.io requests to Ajax but still same problem, I tested site with 32GB Ram, 320GB SSD server and extremely laggy.

There must be a problem with my coding style.