If you have one cup of skim milk with your oatmeal, assuming the oatmeal has absolutely no sugar at all (which isn’t the case), you’d be having 13 g of sugar. I usually like to mix in a spoonful of brown sugar with my oatmeal, adding another 5 g of sugar. Maybe you don’t do that; everyone’s different. Putting in half a banana would add 7 g of sugar.
A packet of Quaker cinnamon flavour instant oats has 10 g of sugar. If you have two packets, it is roughly equivalent to making regular oatmeal with half a banana (7 g), a spoonful of brown sugar (5 g), a tablespoon of peanut butter (1 g) and half a cup of milk (6 g)
Granted, the combination of making it yourself is a lot more nutritionally whole, but if we’re just comparing sugar content, it’s actually not that bad.