Error while painting terrain?

I've attempted to google around for this problem I'm getting how ever, I only found 1 other unity answer which hasn't been answered yet since 2013... sooo I figured I would re-ask.

So I seem to be getting this error: Failed to create Object Undo, because the action is too large. Clearing undo buffer UnityEditor.DockArea:OnGUI()

^This pops up every time I click my mouse attempting to paint my terrain, Now it didn't start when I only have 3 Textures added to my Paint Tool but after adding all the ones I would like to use (around 15-20), I get the error.

Here are some spec's:

Each texture is 10x10. Terrain width and length are 5000x5000. Terrain height is 600. Height map resolution is 2049. and Detail resolution is 1024. Everything else is at default settings in the terrain settings.

My only guess is that maybe the terrain is too large? or something... Any help would be appreciated! Thanks everyone.