Split the file. Cut it into smaller sections using meshmixer or a similar program. Its the supports needed. Turns a small print to a very large print since it has to fill the open air with support material.
Rotate 90 and print with support (just one area will be required). Also, what print ‘depth’ are you printing? For instance, using simplify3D I would use fast instead of high. Because of the flat, 90 degree structure, you really will not gain much. Also, print at a layer height of say 0.1-0.3mm. Much lower does not gain a lot but does increase print times. If you want a nice smooth surface, let the print sit in a acetone vapor contained are like a box and it will make the sides nice and smooth.