Resized 5 x 6 cropped photo to 20 x 24

Hi,

I am trying to make a poster for a Memorial Service - want a 20" x 24" poster.

I cropped a 5 MB picture to the 5 x 6 dimension -- which ended up being about 500 KB.

Then I resized it to 20" x 24" with image resize in  PSE14.

The resulting photo still looks great, even when zoomed, and the Pixel sizes are 4000 x 4800 = 19.2 MP.

But the resulting file is only about 2.5 MB -- is this possible, reasonable.

Claudette in round rock