Efficient building collision/validation

I'm trying to set the texture of the building marker being placed to RED if it is in an invalid position, GREEN otherwise. I've invoked a Con::executef function when On3DMouseDown is invoked in the GUIRTSTSCtrl and I named it 'OnMouseMove' and I passed the position parameters to it.
Here are the 3 rules of validation and how I currently implement them:

1-) Building should not be on water (Check if Z is < 255)
2-) Building should be on flat terrain (Loop over some points between the X and Y limits of the worldBox of the object and store the maximum and minimum terrain height. Invalid if the difference is more than 3)

%worldBox = %b.getWorldBox();

%minH = 1000000;
%maxH = 0;
	   
for (%x = getWord(%worldBox, 0) ; %x < getWord(%worldBox, 3) ; %x += 2)
	for (%y = getWord(%worldBox, 1) ; %y < getWord(%worldBox, 4) ; %y += 2)
	 {
	   	%z = getTerrainHeight(%x SPC %y);
	   	if (%z < %minH) %minH = %z;
	   	if (%z > %maxH) %maxH = %z;
	 }
if (%maxH - %minH > 5) return 2;

3-) Building shouldn't intersect any other building. (I do the same with the terrain with some point in all the other buildings)

%worldBox = %b.getWorldBox();
   		
for (%i = 0 ; %i < Buildings.getCount() ; %i++)
{
   			
   	%t = Buildings.getObject(%i);
   	%box = %t.getWorldBox();
   			
   	for (%x = getWord(%worldBox, 0) ; %x < getWord(%worldBox, 3) ; %x += 2)
   		if (getWord(%Box, 0) <= %x && %x <= getWord(%box, 3))
	   		for (%y = getWord(%worldBox, 1) ; %y < getWord(%worldBox, 4) ; %y += 2)
	   			 if (getWord(%Box, 1) <= %y && %y <= getWord(%box, 4))
	   			 {
	   				%coll = %t;
	   				 return 3;
	   			}
	   				
}

Of course this is tooooooooo slow. I can do some box intersection when testing collision with other bulidings which would be more efficient, but I'm sure that torque provide a method to check for buildings collision.
Any suggestions are highly appreciated....