when to rasters have different cell sizes, the raster calculator will internally resample the rasters in order to have pixels of the same size. You can select the type of resampling in the environment settings of your geoprocessing tool, using:
same as one layer
In your case, you don't have a pixel size that is a multiple of the other cell size. Therefore the resampling will be lossy if you use a pixel size from your layers.
If you want full control on how the substraction will be done, I recommend that you first resample each image with one by one pixels (chosing bilinear or cubic interpolation to avoid "stair like" artefacts and snapping the extent of the first raster to the second raster). You can store those rasters in_memory if they are not too big to avoid duplicating your data.