From the Gnus FAQ (see How do I read news under Emacs?):
If you have a slow machine, or are just really impatient, there are a few things you can do to make Gnus run faster.
Set
gnus-check-new-newsgroups
andgnus-check-bogus-newsgroups
tonil
to make startup faster.Set
gnus-show-threads
,gnus-use-cross-reference
andgnus-nov-is-evil
tonil
to make entering and exiting the summary buffer faster.