Texture sizes affect gpu or only ram?

Noob question but do texture sizes affect material performance on the gpu or only on ram?

My game is only running at 15fps I’m aiming for 30fps, most the materials have 4k textures, would lowering them all to 2k or even 1k increase gpu performance? gpu is my bottleneck

most of my materials have around 150-200 instructions but I don’t have that many meshes, they are large meshes that take up a large portion of the screen though if that makes any difference. My bottleneck is the gpu, mainly the basepass which I don’t really fully understand what that even means but would lowering texture sizes help?