Note that thread is about the [scale] tag, which allows you to have some images at a different scale than the others. If you are loading a large number of images at once, you may want to scale all of them down. For that you'd export to JSON and import it back into a new project, setting the scale during import, described here:
Import - Spine User Guide: Scale
You can use smaller (or larger) images in Spine than you use at runtime, though if your images are so large they cause performance issues in Spine, they may also be too large at runtime.
80 skins isn't very many, especially if you don't show them all at the same time. Your performance problem may be because you show many large images. If you show a screenshot of your Metrics view, that would help.
