Expansion of Model Sizes

I have over 100mb free and I upload a 20mb model and immediately blow my storage limit. I know it creates json model file but even after I delete the original .fbx file I am still over the limit. Is there anyway to get a 20mb model to stay that size when uploaded?

20mb, for a model - is really A LOT.
When you upload fbx or other formats, they have to be prepared for runtime: json - contains vertices and other buffer data, materials will be created separately. And fbx can contain textures as well.

20mb of pure json, is something that web usually won’t handle as single model.

20MB would be a lot if no textures were contained within. One thing to check is that your FBX files are serialized in a binary format. ASCII based FBX files are far, far larger and will eat up your storage space unnecessarily.