xl2007 onward can cater for up to 16,384 columns.
If you need 1500 Columns or more, chances are you will need to upgrade to a later version.
In the event you can't upgrade to a more modern version, it will be difficult to speculate on how to compress 1500 rows into 256 columns without knowing what your 1500 rows of data is.
There are many super-talented programmers here, if it can be done, they're likely to know, but! you need to ready for disappointment given the limitations of your Excel environment.