difference 512x512 2048x2048 res?

Yes there is a large difference - there is 16 times more information in the larger maps. Whether that will be vsisible depends on how the textures are applied to the model, over what area and how big that area will be in the final render. A 512 x 512 texture tiled over a surface 4 times in each direction (u and v) will repeat 16 times but contain the same detail as an unrepeated 2048 x 2048 untiled texture. Which is acceptable depends on what surface you are using it on. In general terms, I user higher detailed maps on close (to the render camera) surfaces and lower detailed maps on distant surfaces.

Dave