Sorry for the mistake, but it’s a technical challenge to generate a 15000-word text in a single instance due to the output character limit per prompt for AI. However, I can provide a smaller piece here:

##Steps to Prepare Perfectly Portioned Overnight Oats

Firstly, the key to perfectly portioned overnight oats lies in three essential components: the oats themselves, the liquid in which they soak, and the toppings you choose to enhance their texture and flavor.

###Select the Right Oats

Your selection of oats will inevitably impact the consistency and nutritional content of your overnight oats. The most commonly used oats for this purpose are rolled oats (also known as old-fashioned oats). These oats have been steamed and then rolled into flakes, giving them a flat, disc-shaped look. Their thickness allows them to retain a fleshy, hearty texture even after a prolonged soaking period.

Steel-cut oats could be a viable option if you prefer your oatmeal with a chewier texture. Bear in mind that they will demand a longer soak time than rolled oats, due to their denser structure. On the other hand, quick oats, as the name suggests, prepare faster but may yield a somewhat mushier consistency in your overnight oats.

###Decide Your Liquid Base

The second main component of your overnight oats would be the liquid you use to soak your oats. There is an assortment of options you may go for encompassing both dairy and non-dairy alternatives. Milk, almond milk, coconut milk, and yogurt are some popular choices.

As a rule of thumb, the liquid-to-oats ratio should be 2:1. For each portion (half a cup) of oats, use one cup of your chosen liquid. If you prefer a thicker texture, you may reduce the liquid slightly. Conversely, add more liquid for a soupier consistency.

###Level-up Your Overnight Oats with Add-ins

The add-ins are what truly add flair to your overnight oats. Sweeteners and spices, fruits, and seeds, all make appealing add-ins. Sugar, honey, or maple syrup can be used to lightly sweeten your oats. For spicing, you cannot go wrong with ceylon cinnamon, its warm sweetness goes hand-in-hand with oats. Vanilla extract is another excellent add-in to ramp up the flavor profile.

Fruits give a fresh, juicy burst to your oats, and can either be mixed in before the oats sit overnight, or can be added in the morning. Berries, banana slices, peaches, or apples all make delightful additions. Dried fruits like raisins or apricots can be a good choice as well.

Seeds and Nuts are a great way to pack in some protein and healthy fats. Chia seeds, flax seeds, sunflower seeds, or chopped almonds or walnuts can add a crunchy texture.

###Preparing Your Overnight Oats

Ensure to mix everything thoroughly. As oats tend to settle at the bottom, make sure to mix them well with the liquid and other add-ins. After the mixing, cover the container with a lid or cling film and let your oats sit in the refrigerator overnight (or at least 6 to 8 hours). The chilling time allows the oats to absorb the liquid and soften while the flavors of the add-ins blend nicely.

By the morning, you’ll have a ready-to-eat, nutritious, and delicious breakfast. You can choose to enjoy it cold straight from the fridge or warm it up in the microwave if you prefer it hot. Adding a splash of more liquid in the morning might be necessary if the oats seem too thick.

###Maintaining Portion Control

Remember, while oats make a healthy breakfast option, portion control is vital to reaping their benefits while maintaining a balanced diet. A serving size of half a cup of dry oats, which results in about a cup of soaked oats, is usually enough for a satisfying meal. Top your oats with your favorite fruits or nuts, but be mindful of the quantities as toppings can add up quickly in terms of calories.

In conclusion, creating perfectly portioned overnight oats is a manageable task once you grasp the essential elements and the process. The delight of waking up to a ready, wholesome, and delicious breakfast is indeed worth the little effort.

For more complex overnight oats recipes and variations, always be willing to experiment and find what combination works best for your taste buds and dietary requirements. After all, part of the joy of cooking is the endless possibilities and the delight of personalization. Above all, enjoy your nutritional, homemade, perfectly portioned overnight oats.