Sqlite batch insertion becoming slower after deployment to client's machine

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C#

SQLite

I have a C# windows application, sometimes the application would be used to import records from excel file, i could import 2500 records in one minute using batch insertion on my development machine, when i tried normal regular insertion approach, it also took the same one minute to insert 2500 records, this get worse after i have deployed the application and installed on a client's machine, it took more than two hours to import same number of record, i just felt since i am using bulk insertion, the speed should be greatly optimised, below is my code:

What I have tried:

public int InsertTaxRecordBatchTransaction(IEnumerable<EmployeeDetails> employeeDetails)
       {
           SQLiteConnection conn = null;
           SQLiteCommand cmd = null;
           var results = new List<int>();

           try
           {
               string insert = "INSERT INTO IncomeTax (OrganisationId,OrganisationName,StaffId,StaffName,Department,Position,NoOfMonthsWorked,TaxIdNumber,SessionId,Month,Year,BasicSalaryVALUES (@OrganisationId,@OrganisationName,@StaffId,@StaffName,@Department,@Position,@NoOfMonthsWorked,@TaxIdNumber,@SessionId,@Month,@Year,@BasicSalary);";
               using (conn = new SQLiteConnection(connstring))
               {
                   conn.Open();
                   using (var transaction = conn.BeginTransaction())
                   {
                       try
                       {
                           using (cmd = conn.CreateCommand())
                           {
                               //cmd = new SQLiteCommand(insert, conn);
                               cmd.CommandType = CommandType.Text;
                               cmd.CommandText = insert;
                               cmd.CommandTimeout = 900000000;
                               cmd.Parameters.Add("@OrganisationId", DbType.String, 50).Value = OrganisationId;
                               cmd.Parameters.Add("@OrganisationName", DbType.String, 50).Value = OrganisationName;
                               cmd.Parameters.Add("@StaffID", DbType.String, 50).Value = StaffId;
                               cmd.Parameters.Add("@StaffName", DbType.String, 50).Value = StaffName;
                               cmd.Parameters.Add("@Department", DbType.String, 50).Value = Department;
                               cmd.Parameters.Add("@Position", DbType.String, 50).Value = Position;
                               cmd.Parameters.Add("@NoOfMonthsWorked", DbType.Int16, 5).Value = NoOfMonthsWorked;
                               cmd.Parameters.Add("@TaxIdNumber", DbType.String, 5).Value = TaxIdNumber;
                               cmd.Parameters.Add("@SessionId", DbType.String, 20).Value = SessionId;
                               cmd.Parameters.Add("@Month", DbType.String, 20).Value = Month;
                               cmd.Parameters.Add("@Year", DbType.String, 20).Value = Year;
                               cmd.Parameters.Add("@BasicSalary", DbType.Decimal, 2).Value = BasicSalary;

                               foreach (var employee in employeeDetails)
                               {
                                   cmd.Parameters.Add("@OrganisationId", DbType.String, 50).Value = employee.OrganisationId;
                                   cmd.Parameters.Add("@OrganisationName", DbType.String, 50).Value = employee.OrganisationName;
                                   cmd.Parameters.Add("@StaffID", DbType.String, 50).Value = employee.StaffId;
                                   cmd.Parameters.Add("@StaffName", DbType.String, 50).Value = employee.StaffName;
                                   cmd.Parameters.Add("@Department", DbType.String, 50).Value = employee.Department;
                                   cmd.Parameters.Add("@Position", DbType.String, 50).Value = employee.Position;
                                   cmd.Parameters.Add("@NoOfMonthsWorked", DbType.Int16, 5).Value = employee.NoOfMonthsWorked;
                                   cmd.Parameters.Add("@TaxIdNumber", DbType.String, 5).Value = employee.TaxIdNumber;
                                   cmd.Parameters.Add("@SessionId", DbType.String, 20).Value = employee.SessionId;
                                   cmd.Parameters.Add("@Month", DbType.String, 20).Value = employee.Month;
                                   cmd.Parameters.Add("@Year", DbType.String, 20).Value = employee.Year;
                                   cmd.Parameters.Add("@BasicSalary", DbType.Decimal, 2).Value = employee.BasicSalary;

                                   results.Add(cmd.ExecuteNonQuery());
                               }

                           }
                           transaction.Commit();
                           DspMsg = "Tax computed successfully!";
                       }
                       catch(Exception ex)
                       {
                           transaction.Rollback();
                           DspMsg = ex.Message+ " some errors have occured, no record was saved! ";
                       }
                   }
               }
              // conn.Close();
           }
           catch (SQLiteException ex)
           {

               DspMsg = ex.Message;
           }
           return results.Sum();
       }