循环运行缓慢

我有一个Web Method，它正在查询Outlook以从Global Address List获取所有通讯组列表。

这将获取4000多个分发列表，这正是我希望它做的，但当它进入循环将4000个列表传递到我的List时，它需要3分钟以上才能完成for循环。有人能看到任何不同寻常的事情吗？有人能回答为什么会发生这种情况吗？

这是我的代码：

        public class DistributionListDetails
        {
            public int DistributionListId { get; set; }
            public string DistributionListEmail { get; set; }
        }
        List<DistributionListDetails> distributionLists = new List<DistributionListDetails>();
        int val = 0;
        //create Outlook application. 
        Outlook.Application oApp = new Outlook.Application();
        //get Mapi NameSpace and Logon. 
        Outlook.NameSpace oNS = oApp.GetNamespace("mapi");
        //get Global Address List. 
        Outlook.AddressLists oDLs = oNS.AddressLists;
        Outlook.AddressList oGal = oDLs["Global Address List"];
        //get a specific distribution list. 
        string sDL = "TestDL";
        Outlook.AddressEntries oEntries = oGal.AddressEntries;
        Outlook.AddressEntry oDL = oEntries[sDL];
        if (oDL.Manager != null)
        distributionLists.Add(new DistributionListDetails
            {
                DistributionListId = val,
                DistributionListEmail = oDL.Manager.ToString()
            });
        //get all of the members of the distribution list. 
        oEntries = oDL.Members;
        Outlook.AddressEntry oEntry = default(Outlook.AddressEntry);
        int i = 0;
        for (i = 1; i <= oGal.AddressEntries.Count && i <= 10; i++)
        {
            oEntry = oGal.AddressEntries[i];
            distributionLists.Add(new DistributionListDetails
            {
                DistributionListId = val,
                DistributionListEmail = oEntry.Name
            });
        }

注意：我通过AJAX将循环中返回的列表绑定到下拉列表中。

distributionLists.AddRange(oGal.AddressEntries
  .Cast<Outlook.AddressEntry>()
  .Select(
    x => new DistributionListDetails 
    { 
        DistributionListId = val, 
        DiestributionListEmail = x.Name
    }));