Regarding size of json

while converted from fbx to json . size is too large about 48MB.
and also imported scene is around 84MB.
is there anyway to reduce it.

If you have gzip enabled on the server (if you publish to PlayCanvas, it does have this enabled), that will compress down to a much smaller size on download to the user. (a quick test shows that table and chairs (48MB) that it compresses down to ~10MB).

I will add that you’ve uploaded a model that technically is not real-time rendering friendly, especially not for WebGL.
What you want is to have as optimized geometry as possible. Having 500,000 triangles for something that should have as little as few k’s, is way way too much.

It is important for any WebGL development to keep assets small and optimized.

i want to download and host it on my server. but the size is greater on download.

As @yaustar mentioned, if you enable GZIP on your server then it will be much much smaller.
Download size - is uncompressed. When it is server from web server with GZIP it will compress content so browser downloads less and decompressed on receive.

But as mentioned, such large file sizes, are not suitable for web served content.