I don't do much about this myself, but I thought I'll try to pass this feedback from the Hebrew Wikipedia along.

The JSON code added by "Insert graph" is rather complex and long. In some Wikipedias there is a template (with Lua backend) which can insert a <graph> with essentially the same content with much less code: https://en.wikipedia.org/wiki/Template:Graph:Chart

It would be nice to try to reduce this code to something more manageable.