We have one large content database, consisting of two site collections with 250 GB space . 

We have deleted one large site with 100 GB size from content database using gradual site delete job.

The gradual site delete job is running every day and running just for 1 to 2 minutes.

The Job history is showing it is running on the desired content database where our deleted site was hosted,  but ending within 1 to 2 minutes .

Noticed that unused space in content database is increasing and the content database table rows are getting changed.

Before Deletion: 
Alldocs - 17112725
AllLinks - 15537151
NameVluePair - 16992586
storagemetrics - 17112723
alluserdata - 1678086
doctostreams – 5867519

After deletion table with rows.

Alldocs - 1570168
AllLinks - 7728077
NameVluePair - 8
storagemetrics - 1570168
alluserdata - 1375680
doctostreams - 2553731

Note--content database is hosting another site with 100GB data.

how we can  confirm whether this job is running and deleting the site content with complete data of 100 GB  from content database?
How long it will take to completely delete the content.