sorry you are feeling awful!
I think the starting to feel sick/vomit at 15 weeks is probably less common, for most women who experience N&V (nausea & vomiting) it starts at around 6 weeks, intensity peaking at 9-11 weeks, then declining by 12-13 weeks.
but as you say it varies, from person to person and from pg to pg for the same woman!
a friend of mine was sick every day through her whole pg, from the day after she conceived till the day baby was born.
others never even feel nauseous (lucky bastards, call themselves pregnant, pfft!
)
my worst experience of morning sickness was with DS3 - N&V from 5 weeks till 16 weeks. it peaked at 10-13 weeks with me being sick up 5 times a day.
after a few months of being well, N&V returned at 7 months and stayed with me until the day before he was born. the last week of pg was particularly horrendous.
my dear DS3 made up for it though as I had fab time giving birth - having had gentle contractions for about 20 hours, at 5am the contractions went boom, unbearable. we got to the hospital at 6am he was born at 6.35 am with 3 pushes!
I was physically sick only twice (2 days apart at 11 weeks) with DD through the whole pg, very easy.
others were in between in length and intensity.
I hope it will ease/disappear soon, I know you are desperate to feel better!
I took brewers yeast with DS3.
drank lots of fizzy drinks to help me burp, which eased the pressure in my tummy.
ginger can help too
you probably have your own tricks already.
big hugs - well small hugs, I don't want to squeeze you! 