Changing IP of msloop
Can't help with the speed question but some generic remarks:


Both ManagementClass and ManagementObjectCollection are IDisposable and should therefore be wrapped in a using block to make sure any unmanaged resources are properly released.
Prefixing all your local variables with obj smells like hungarian notation and is generally discouraged. It adds not value and just clutter. Your variable names should indicate what they represent and not what type they are.
In C# land the common naming convention for methods is PascalCase and not camelCase. It pays to stick to general naming conventions for the ecosystem you are working in as it will make your code look more familiar to other developers.