That's texture size, not texture memory. Increasing texture size will eat more available memory, which you cannot increase.
I actually had to reduce some texture sizes as increased game resolution (or SSAA) beyond a certain level because the game could not allocate enough memory for everything and was starting to reduce LOD on, or would fail to load, certain textures.
4k planetary/galactic textures work fine up to around 2560x1440, but I'd limit the use of 8k textures to 1080p or below. I personally use 3072 texture sizes at 1440p to ensure there is never any texture anomalies and keep minimum frame rates up.