Speed up reading and simple parsing of large text file in Swift

I have a small piece of code that reads in an ASCII Autocad dxf file. This needs to be read into an array of structs where the struct is an Int and a String. For small files the way this is implemented is fine. But for large files, ~12.4 GB, it grinds to a halt taking about half an hour as the amount of memory required explodes to ~75 GB. Looking for someone to rewrite this class / function to it run much, much faster and has a smaller memory requirement. Current Code and small example file attached. The large model is here: [login to view URL]