Painting kitchen water base on top of oil base?

I'm very surprised the salesperson didn't tell you about that. Yes that is the reason it is peeling. You should have lightly roughed up the surface of the walls using a 150 grit sandpaper. Wiped it down using a little a little ammonia,dawn dish soap,and water, on areas like around light switches . Then you should have used an oil based or a water based primer such as Kilz. Doesn't matter which one you do use but for a kitchen, an oil based would be best. Then after it has fully dried, you can go ahead and paint with your water based paint. You can put water based paint over an oil based primer but not over an oil based paint. Also when you rough up the surface, you don't need to do every inch of the walls. Just a quick go over. Usually when I told customers that they had to sand, they would give me a look like they had just eaten a rotten egg or something. You don't have to do it till your arms fall off.If you have,or can borrow a electrical sander it would make the job a little easier. Don't use TSP unless you read and understand their directions.. You must completely rinse if off with water before continuing. There is another product you should look at. That is Liquid Sandpaper. I have never used it but I have heard good things and not so good things about it. You will have to look at the label before buying it. Hope I helped out. Good Luck