How can I align 2 holes 1.5m apart?
Borrow a laser level
Borrow a 4 foot mason's level
Don't use a level -- use a plumb bob and HS geometry 


Make a plumb bob by hanging a heavy and centered weight from a chalk line and snap it in the center of your desired holes..  Now pick a point on the wall that will be your left hole and two points on your chalked line.  Use a wire and measure the distance from the hole to the upper point on your chalk line.  Draw an arc on the opposite side of the wall.  Repeat for the lower point on your chalk line; where they intersect is the location of your other hole.