SQL Server moving to new file

Solution 1:

One thing to try is shrinking the existing file in small increments, it may take many passes to get it down, but it usually works; 10GB per pass is a good number to try.

If not, and you are trying to add another smaller file, you'll need a file large enough to hold the used space in the current file, which I assume would be around 600GB (40% used * 1.5TB), add the file to the existing file group and use the option in SSMS to "Empty file by migrating the data files in the same filegroup" on the current larger file. It's going to take a long time with that much data. When it's all done, you should be able to remove the existing 1.5TB file.