oh and it only runs at 25% usage
What effects are applied?
25% CPU or 25% GPU?
cpu, like 1% gpu. what is wrong?
Assuming a proper hard drive configuration, there's really only two things you can do to speed up exports, all else being equal.
1. Turn on GPU processing.
2. Get faster hardware.
I don't think either one of those applies here, so...
Disable integrated graphics, go to device manager and disable the intel one installed.
Update nividia drivers, go the nividia control panel and enable it for all apps and you can customize a few things for high performance.
Close the apps, go to there folders( c: adobe\premiere) and find the sniffer.exe
Go back to premiere , re enable mercury /cuda.
It also helps using multiple ssd drives.
Either way that should help.
I did this and was able to render a 12 minute A/V sequence, with titles, motion graphics, color grades, and effects and finished in under 10 mins. I have the same rig and export config as you.