It is actually normal that PCs slow down a bit, though 5 minutes is way too much to be usable.
Troubleshooting:
Check startup load is not excessive. 8GB of RAM are enough in most cases but are not a lot. Go under Task manager -> Startup and check what apps are enabled to launch and their incidence on performance. Installing apps usually turns computer startup slower as more processes are added at startup.
Check maintenance:
Clean up disks via the cleanup utility in windows
Defrag Hard disks (to be done after above step).
Let me know if anything helped. Consider also switching to SSD for the main partition if you are not currently using one.