The processing time is independent of the scale of the texture.
Actually a smaller texture is faster since there's less memory to read (and depending on the read pattern, possibly less texture cache misses), but in this case the difference miles from noticeable.
Also, the textures are not scaled on your GPU they are sampled. The processing time is independent of the scale of the texture.
Maybe he meant scaling the texture to a power-of-2 instead of padding to power-of-2. There's no need to stick power-of-2 sizes anymore.