A few questions:
Yes, it is possible to delete page types from admin but only under certain circumstances. In order to delete a page type, the following must be true:
If those requirements are met, you should be able to find the delete button by clicking on "settings" on the type.
To see a list of pages by type you could create a plugin to pull that information out programmatically though, as luck would have it, Nicola Ayan has done the hard work for you here:
Alternatively, if you are using Find on your site, you can look at the contents of the index from Find > Overview > Explore.
I installed the plugin and it seems to be working great!