Is it worthwhile to setup HTTP 2 reverse proxy in front of HTTP 1 server?
Solution 1:
This is one of the scenarios Nginx explicitely supports, and you would most likely see at least some performance gains due to the improved pipelining, having only a single TLS session to negotiate, etc... assuming your application's architecture is such that it would profit from those benefits.
However, beware that some of the oft-used HTTP 1.1 hacks you may have implemented to optimize your performance in the past (e.g. domain sharding, image sprites...) are actually counter-productive with HTTP2, so you may want to tweak your config such that they are only used for HTTP1.1 clients.
These points are addressed in greater detail here : https://www.nginx.com/blog/7-tips-for-faster-http2-performance/