No it won't, unless you're doing something stupid in your app, such as using synchronous or CPU-heavy code. But putting nginx in front of it doesn't save you here either; you'd need a caching reverse proxy instead.

The only thing where nginx might help performance-wise here is static file access (of eg. static web assets such as CSS or static HTML).

Hm, I use Nginx mostly for routing and static files and not for performance reasons.