I would doubt it would be free - the sauce for the prawns would probably contain oil or some other kind of syn. I do think it sounds like a reasonable choice though, although I couldn't say how many syns it would have in it!
Would it not be easier for you to make this yourself, that way you know exactly whats going in to it, tomato based sauces are very easy to make!
I could understand getting a chinese for like black bean or sweet n sour etc but you could probably make that dish yourself and it might even be nicer!!
Anything ordered from a takeaway is likely to contain oil, even the healthiest sounding options! However I'm sure this dish would be under 10 syns, perhaps you could ask how it is cooked so that you could work out its syn value? I often do, as it is the only way to know for sure. You may be plesantly surprised!