As a user of Bundler Show archive.org snapshot you have spent significant time looking at this message:

Fetching source index for http://rubygems.org/

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

• Prevents you from data breaches and liability risks
• Upgrade at your own pace
• Works with modern Rubies

Read more Show archive.org snapshot

To make Bundler skip this index update and only use installed gems, you can use the --local option:

bundle install --local

Unfortunately this does not work with bundle update.

It is said Show archive.org snapshot that Bundler 1.1 will use a feature of Rubygems.org that allows partial index updates. Hopefully the whole issue will go away with that.