If I remember correctly I tried Atom before VSCode as I thought: well, that's a nice looking editor. But oh, it was just unusable for such a large file.
Smartphones from a couple of years ago already had multi-core, multi-GHz processors, and 2 GB or more of RAM. A 6 MB file would fit into memory well over a hundred times, even assuming lots of overhead.
Any moderately reasonable text editor should be able to handle a file of that size with total ease, at least for the basic operations.