I don't think flaked or torrefied wheat offer a significant advantage over malted wheat. And commercial Weißbier certainly uses malted wheat - at least 50% by law, and in most cases hardly more than that (due to the brewing process).
Wheat, in any shape, does not increase the body. I'd even say it adds less body than pilsner malt, certainly less sweetness. Munich malt gives a nice impression of maltiness. 15% seems good. If you want more body, I'd suggest something like 40/40/40 wheat/pils/munich, but that would probably be detrimental to head retention.
Something to try: step mashing with a short (15 mins) protein rest, maybe a simple decoction. I wouldn't expect a huge difference, but it could help. As always, mash pH is important as well.
You haven't told us the OG of your recipe, which may be an important factor here. Going for 12.5 to 13 degrees plato (1.050-.1052), possibly even a bit more, should give plenty of body.
Keep the bitterness low (10-15 IBU, I think). Some recipes call for aggressive carbonation, which certainly is not inappropriate, but I prefer them a little softer. (Maybe I'm just a bit sensitive to the "carbonic bite"). Last but not least, glassware and pouring technique are important.