Http/2 send very slow

[VrasidasP]

We wanted to update our PushNotifications service by sending with Http/2, but it takes way too long compared to the normal (binary) method.
For about 15000 devices, binary method takes about 2 minutes to finish. We haven't been able to finish such a large request using http/2, it takes at least an hour...

Why is this happening?

[yetdog]

I'm working on the 2.0.0 alpha release for HTTP/2, and I wouldn't say it's "at least an hour" slow, but it definitely seems a bit slower than the binary method....