If
and you worry about
I suspect that the array is quite large and that updating the price is a frequent use-case.
If it is the case, then for performance reasons you might want to completely go away from embedding stock_prices in your main documents. Somewhere in the storage engine documentation you will see than when a document is updated the whole document is written back to disk. So despite the fact that you may access/update easily the prices your performances might be hindered by writing to disk the whole array/sub-document.
I think it is worth investigating moving stock_prices in its own collection and to use $lookup to present the results in its current format. I think it would have a lot more impact in your update performance compared to the current schema.