Admittedly 8GB does sound a bit on the light side.
But a 'clean boot' doesn't necessarily mean there is nothing running in the background. You may not have actively launched any app's, but there's always stuff going on in the background. There have been numerous discussions about it.
Try this for starters- can't hurt...
1) Go to Apps options and manually select all apps, and disable notifications for every single app you can.
2) Go to App Store and disable automatic updating of all apps, by clicking the 3 dots on the top corner.
There are other tweaks to reduce the workload on the processor but these seem to make the most sense. There is also a free app called Zapper App killer which can be useful to quickly shut down any un-necessary processes.