There's various things you can do about this. If you don't care about logs from months ago, you can happily just wipe the older files in /var/log/journal; just look at the file dates to see what date ranges each file covers. You can also just use smarter journalctl commands. The one I use the most often is 'journalctl -b', which is 'show me all messages since I booted'. You can also pass in absolute or relative date ranges (like 'all logs in the last week') and stuff, if you check the man page.