Tool Preset Issue

[Blighty]

Each brush that you create has a native size, in your case 15x15 and 25x25. But lets say that the brush size in your tool options is set to 50. The brush size in the tool options does not change if you select a brush with a different native size, it will remain on 50.

In the tool options, next to the brush size, is a button to reset the brush size to the native size of the selected brush. Click that.

See attached:
http://imgur.com/a/kgQQI