Please remember, DXF files are unit-less so you must tell ACE what DXF
units you wish to use. Here's our guidelines for DXF conversions:
When opening your DXF (in AutoCAD) I measured the extents of 1500 x 1500 which is quite strange so I'm not exactly sure what units to assign. When the DXF is drafted by someone else and units/scale are unknown; there is no exact science. Typically in my experience units are clearly Inch, Millimeter, or Microns; and many times there will be "text" (in a title block or label) in the DXF describing the units and scale. In this case I would suggest trying "millimeter" or perhaps using a scale of 0.5 and "millimeter".
Here's a screen capture showing where to assign the scale and units for DXF Import: