Here is a solution that include folder size and folder size with the size of its subfolders. In line 28 changing "size" to "fullsize" at sort-object you can choose to sort by the total subfolder size.
In the same row I set 100 as the maximum number of results at select-object. You can also adjust it according to your needs.
This code runs on my laptop for about 4 minutes for the root of C drive, so be patient.