By default without any options, the
journalctl is indeed very slow. But usually, we are only interested in some logs and can use options to specify the logs that we are interested to check. This will make
journalctl less slower.
Check the last 100 lines
journalctl -n 100
It will show the most recent 100 journal events.
Check since last boot
journalctl -b -0
Here, -0 is the last boot, -1 the boot before last, and so on.
For more usages of the command, check journalctl manual.