In your example they are interchangeable and mean the same. 'going to' and 'will' are interchangeable and equal when you make a future prediction (or make a question of it as in your example) There can be subtle differences between 'going to' and 'will' in other contexts, but in your example they mean the same. Here's a link if you're interested that talks about it a bit: https://www.grammar.cl/Notes/Future_Will_vs_Going.htm

Nope, they're synonymous. Edit: upon reflection, there are subtle differences between them. There are situations where one feels appropriate but not the other. This page attempts to explain, although I haven't read it through carefully: https://www.grammar.cl/Notes/Future_Will_vs_Going.htm

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