Is there any big difference

between 1600 dpi 0.15 and 400 dpi 0.6 sens?
If i change does it affects my aim too much?

Technically yes

U have to use it to find out if u like it or not, there will be a difference slight but u may or may not notice it

U are gonna be less precise and less responsive

use 1600 dpi

1600 objectively smoother. 400 is only really good for low sens.