gnus-activate-foreign-newsgroups

gnus-activate-foreign-newsgroups is a variable defined in `gnus-start.el'.
Its value is

4

Documentation:
*If nil, Gnus will not check foreign newsgroups at startup.
If it is non-nil, it should be a number between one and nine. Foreign
newsgroups that have a level lower or equal to this number will be
activated on startup. For instance, if you want to active all
subscribed newsgroups, but not the rest, you'd set this variable to
`gnus-level-subscribed'.

If you subscribe to lots of newsgroups from different servers, startup
might take a while. By setting this variable to nil, you'll save time,
but you won't be told how many unread articles there are in the
groups.

You can customize this variable.