(1) Your ingredient list:
200 ml 1.5% milk
10 g vanilla pudding
5 g vanilla sugar
120 g raspberries
is entirely and totally correct, and you should write it precisely like that.
(The only alternate, would be "1.5% milk-fat milk" which would be perfectly understandable, but readers would wonder why you wrote it that way.)
(2) 1.5% milk is almost always referred to as "1.5% milk" in the USA. (Same for other milks, example 2% milk, 1% milk, 0% milk, etc.) This applies to both packaging, written, and spoken AmE. (Naturally, phrases like "low fat milk" are also used.)
(3) You can trivially find any number of examples of this since there are a great number of recipes online, and they are all written the normal and usual way - that way.
(4) Regarding 27% cream cheese. I would suggest it's somewhat less usual to say that (just because, families/etc refer to milk every day ["someone get some more two percent milk today!"] but less often cream cheese. It is perfectly understandable, but it's possibly the case that
cream cheese (27%)
is more common. (Just to repeat, "27% cream cheese" is perfectly understandable.)
(5) In general terms it seems totally commonplace to shorten a two-word adjective ("18/20 chromium steel") to only the key part ("18/20 steel"); there are endless examples and, again, I'm surprised my buddy Chas above is surprised by it.