I make the same with your file (used Zbrush Decimation Master 10% - gives me a file OBJ 1 .5 megas )

But subdiv in Moi gives a 3dm quasi 1 Giga ! (980 megas) not manageable on my Latop! (just following)
https://www.filehosting.org/file/details/790793/Rhino_scan_remk.zip (file 3dm of 980 megas)


with Decimation Master 5 % gives a file OBJ 660 KB for a 3dm of 450 Megas!
https://www.filehosting.org/file/details/790794/Rhino_scan_remk660.zip (file 3dm of 450 megas)
More easy! Just following!