15000 trees over 140 aces is approximately 1 tree per 20x20ft square. That doesn't resemble my own idea of 'forest', but it's not stretching the definition that far.
That seems roughly right for large-ish oak trees, the sort of forest I spent my childhood running around in. Of course there are hundreds of different sorts of forests.
Oaks are so beautiful and grow so quickly. Definitely my favorite tree. Hardwood trees will grow to have wider canopies so that plot size definitely makes sense.