Blurry, low resolution textures

I can’t find a reason, why some of the textures are rendered perfectly, and some not.
In fact parts where are textures of wood are super detailed. No problems.

But the rest is blurry and no matter what I do I can’t achieve a better result.
Here we have 2500x2500 pix. Not too much but still very low quality.

Even if I change it to 1500x1500 still it looks very bad.
I had these kind of problems when I exceeded 4k textures. But never with textures like 1500x1500px.