This isn't even very well formatted as an .epub file.

In order to read it, I had to download it and open it in Sigil.

...To find out how big the actual text was, I then copy-pasted the plain text into Leafpad (a Linux Notepad lookalike) and saved it as .txt; then I could open it in LibreOffice and use the word counter.

It is 5590 words or so.

This is small enough that you could have just copied and pasted the whole thing into the submission edit buffer, which would save everyone having to download a 2.2 MB file. The .txt file I saved was 32KB. As previously noted, you are including all the fonts required to read this which is an unnecessary step.

Of course, using the edit buffer can require a little knowledge of formatting the HTML way but you can use Word or another word processor, the system is smart enough to figure out most input types. "Preview" will always show you exactly what the viewer will see and you can continue to make adjustments until you are satisfied.

If you look in the Forums, you can find help (here, for example) on good ways to lay out your story which won't involve you in too much effort and won't cause too much trouble to your readers. In general, less is better.

Penny