Explain your workflow please. You can’t import what? I know it’s a mesh, but in what format? obj? gtlf? blend? The recommended method is GTLF.
If you are running out of memory it means that the maximum amount of allocated memory has been exceeded, but you would need to provide the exact error as displayed to you in order for us to understand what exactly happened. I presume you just need to increase the memory allocated by default; in which case the documentation provided explains how to do so:
In respect to the time it takes, there’s not a lot anybody can do except increase your processor speed. A mesh that huge will just take time. There’s not a lot anybody can do about that except yourself. Blender (again i presume) is a hugely sophisticated tool. Again - if you provide more information maybe someone can assist you further on that.