All
of the emails in your Gmail account (Inbox, Sent, Trash, Spam, etc) count towards
the storage limit.
According
to Google, the emails in your Trash that are 30 days or older are automatically
deleted, but that is not always the case.
If you are getting close to your 15 GB of Free storage, then you may
want to consider manually deleting some or all of the emails in your Trash.
Use
caution when permanently deleting the emails in your Trash because Gmail uses
threaded conversations as the default so some of the emails in your Trash may
be linked to other emails in your Gmail account (i.e., Inbox, Sent, etc). Before you delete an email in your Trash, you
should open the email and review the emails (i.e., conversations) that it’s
linked to.
Every
Google account starts with 15 GB of Free storage that's shared across Google
Drive, Gmail, and Google Photos. When you upgrade to a Google One membership
plan, your total storage will increase and you will gain some extra benefits depending
on the plan you choose.
Google One Plans