Yes, you sure can. Before setting up the action, resize one of your photos to 1500 pixels wide, then put your logo on it, and take the measurements, blah blah blah, exactly as I've instructed.
The only peculiar thing you have to do is this: When you get to the Fit Image step, enter 1500 for the width and something outrageously big for the height:
This will ensure that every photo is 1500 wide, regardless of shape or orientation.