“will you be sick” or “are you going to be sick” (emesis)

Are you going to be sick if you eat that?

This clause "are you going to" is a future prediction so shouldn't it be better to use will?

Is going to used as the event "being sick" is about to happen very soon.
This sentence is without context, it is an example taken from the website Woodward English
Be going to

Usually 'to be going to' and 'will' are directly interchangeable, but there are times when they are not.

In your example, the are interchangeable.

In the following example the are not interchangeable:

I am going to France for my holiday.

You cannot replace 'going to' with 'will' in that sentence.