Rails 5.2 will integrate bootsnap for faster boot loading loading. On my dev setup, this brings booting time down from 10s down to 6s, which is almost half.

http://weblog.rubyonrails.org/2017/11/27/Rails-5-2-Active-Storage-Redis-Cache-Store-HTTP2-Early-Hints-Credentials/
https://github.com/Shopify/bootsnap

Unfortunately, this cannot be used in Red Hat production because we are not using Bundler on our RPM installations there. For Debian where Bundler is in use, this should work just fine - I haven't measured speed improvement there.