Processor & RAM
The Samsung Galaxy Note 5 comes with a Exynos 7 octa-core processor and 4GB of RAM. The Galaxy Note 4 features a Qualcomm 805 processor in the United States to go along with 3GB of RAM. This should help the Galaxy Note 5 perform better in key areas over time.
The Samsung Galaxy Note 4 and its hardware should still be good enough for most people though so you'll want to go hands-on with both phones and see if you're able to notice any sort of a difference in your daily activities.