No problem. If you want even more control over the player movement. You can always assign scripts to the d-pad.
Like this:
In scene ON INIT script. Assign script to UP on D-pad (for example). Put this code in: Player face direction Up. Then Move Relative X,Y-2. (2 because each y coordinate is 8 pixels, 2 coordinates will move the player up 16 pixels). Do the same for each direction and it would have the same outcome as changing the grid size to 16 pixels.
While it is more work doing it this way, it has the benefit of loads more control over what is happening. You could set the player sprite to be whatever you want when they walk up or down or left or right - so you wouldnt be limited to 2 animation frames for the player characters walk cycle, for example!