It will improve write performance slightly, but make very little difference, if any, to read performance. You might shave a little time off your boot time, but it would be barely noticeable.
20+ seconds isn't too bad. systemd is a replacement for the old init scripts, which can increase boot time a bit, but there are a whole slew of other problems and it might be difficult to install.
Other options are to disable unused services, and look at using hdparm to tweak your hard drive. I've found with older drives this can help quite a bit.
Lastly, make sure you are using noatime, or relatime mount options in /etc/fstab. This stops Linux from updating the access time for every file read, though it may be your system is already not doing this.
But don't disable the journal, and 20 seconds or so boot time isn't too slow.