adding a 53Kb .png image to a 23Kb word file results in a 1.5Mb file

The twist to it is that for some documents the result is a normal ~~ 80Kb but for most it jumps to 1.5Mb. I can’t figure out the difference.

This being a template that is multiplicated hundreds of time, it causes quite a space issue. Basicaly I am trying to add a logo to existing templates.