Time Machine Backups taking too much space?
I would probably do two things: 


Let time machine run until it fills up the 1.6 TB and then see how long a windows you have. macOS will clean up the destination - purging old files as needed. 
Use tmutil compare or a tool like Backup Loupe to check what is taking the space. Other tools do a lousy job of showing you actual space usage in time machine. 


Why does Time Machine estimate a 109GB backup size, but then need 235 GB?
Time Machine - List of Files that were backed up