@fns/Vlad, what version of Spine are you using? Are you packing an atlas when you export the JSON? Do you have Pretty print checked? If so, try unchecking it.

The only reason to use JSON is if you need to read the data. Otherwise you should be using binary, especially if you have a large project. Please check if a binary export succeeds.

As a last resort you can increase the maximum amount of memory Spine is allowed to use by running it this way (for example, for 4GB):

Spine -Xmx4096m