create_snapshot performance issue?

Hi!

This _may_ be more of a question than a validated bug.

I have a moderately complex schema, and an XML file of ~1000 elements. I see a bit over 800000 calls to `.create_snapshot()` for a `.deserialize()`, and over a second to parse that document (with `lxml`). This seems … excessive.

Not sure what context to give here to make this clear.

Thanks!