I think what you should be looking for is:
Model.Content.AncestorOrSelf(2).Name
Model returns a RenderModel object but what you want is the IPublishedContent object which you will find in the Model.Content
property.
You should of course perform a null check before attempting to access the name e.g.
if(Model.Content.AncestorOrSelf(2) != null)
{
sectionTitle = Model.Content.AncestorOrSelf(2).Name;
}