Question about Hoooked Zpagetti

I ordered this because the needle recommendation was 12-15mm, but the needle recommendation on the package was 12mm. I also ordered other shades and for some, the needle recommendation on the package was 12mm, for others, 12-15mm. Are there two sizes here? I meant to use multiple yarn balls to make one large blanket, but this is impossible when the yarn size is so different that the gauge is different for the 12mm and 12-15 mm. Do you get different yarn sizes everytime? (In that case, you should make a point about that somewhere, otherwise all knitting projects would have to be limited to what can be done with 1 ball of yarn).