The JSON is from 2.1.27, so you will need to use that version to import the data. You can run Spine with
-Xmx1200M to give Spine more memory. 1200 MB is around the most Windows will give because 2.1.27 is 32-bit. Spine 4.0+ is 64-bit so can use much more memory, but won't be able to read the old 2.1.27 JSON data.
If you have the
.spine files, that would be best. Worst case I guess you could use a text editor to delete some of the animations. Find the
animations section, identify each block that is one animation, and delete some until you can get it imported without running out of memory.