Photoshop image size question

The question to you what file format are you saving.  You should be saving a flat images like  a Jpeg imags with a high quality setting 10,  11  or 12,  You want to submit a high quality image that has a large number of high quality pixels.   The jpeg compression will reduce file size and if you are editing in 16Bit Colot converting it to Jpeg 8bit color will half the file size.  You do not want to save a layered file they will be large. If you insist on submitting a 16 bit color image  save a Tiff but not a layered one.  And save it with compression.  If you have a large number of pixels you would most likely have the document Print resolution set much higher the 96PPI. So the  print will not be huge be more normal in size like a high quality 8" x 10" print. A  8"x10" 300ppi image has a width of 2400px and a height of 3000px.    A  3:2 Aspect  Ration Raw image from my 16MP camera  has an image  4896px by 3264 px and prints 9"x6" with a 544PPI. The bulk of an image files size is Pixel data,  How well the pixel data in an image will compress depends on Image content.  How much detail the image has.  A blue sky will compress very well a cloudy sky will not compress as well there is a lot more detail to that sky.