If you thought customizing certain aspects of the homescreen was just for those using third-party home launchers downloaded from the Play Store, once upon a time you might have been correct, but that isn't the case anymore. With how far Android has come, customization features have been one of the best parts about Android as a mobile platform. This includes altering the grid size of the home screen to allow more app shortcuts, and this is a function you can find on the new Samsung Galaxy S6 and Samsung Galaxy S6 Edge. It's also easy to access and change this particular detail if you're interested in tweaking things just a little bit.
Out of the box the device will come with a default homescreen grid size of 4 x 4. While this may be plenty of screen space for the average user, for anyone who tries to maximize the amount of space they have by adding all the things they use to the homescreen, a slightly larger grid size might be needed. As such Samsung has added the ability to change things to either a 4 x 5 or 5 x 5 grid as well. It might not be as versatile as the options given to you by something like Nova Prime, but it's a good start for a stock OEM launcher. To get to these options users simply need to long press on the home screen or pinch-to-zoom to bring up the homescreen edit options which is where you'll find screen grid next to wallpapers, widgets, and themes.
From here just tap the screen grid button which will open up the three different grid size options, select as desired and proceed to apply the shortcuts for apps or apply the widgets in the new empty space you've been given. If some widgets you already have on screen become smaller, you may be able to just resize them to fit the new grid size although this will vary from widget to widget. That's all there is to it, now you can add more space to the homescreen as needed.