Scared to gain weight, I don’t want to get fat but don’t know how many calories I should eat.

15K steps is at the upper limits of very active. It will exceed very active calories way more times than it will fall short of them. Assuming you track to the population norms. And that your intake is accurate-ish.

You are being slightly coy in terms of coming up with your hard and actual numbers.

Your exact deficits and weight level changes over months, not a single week, will give an indication as to whether there exists Adaptive Thermogenesis at play and the level of AT, if any, that we may be dealing with. Your actual intake and weight level changes will give closer to actual numbers. All this, of course, depends on the "quality" of your logging.

BUT, you're giving general numbers (I ate about 2000, I lost about a lb, I am only disclosing the last week), and "demanding" precision for an answer.

So, the answer remains: eat 3,000, evaluate your weight trend after 3-4 weeks if male 4-6 weeks if female. Adjust as and if needed.

You're angling to hear don't eat more than 2,500. This is called bargaining. And fear.

You're BMI 21.5 and 20 years old. There is no rational reason why you would be scared to increase your calories.

You're the one increasing them. You're the one regulating your intake and exercise output. You are not a passive observer.

If you are unable to act because of irrational fear, then you ought to be looking into getting some help, right?

There is a very good likelihood that when you increase your caloric intake you will also be increasing your unconscious (and autonomic) expenditure and that your most current losses (if at the tail end of a long duration or high deficit restriction) are under-representing the calories you would have to eat to balance.

There is a very good likelihood that when you increase your calories and eat more, due to volume of food and replenishment of energy stores you will show an immediate scale increase.

If you are not eating at the balancing point you will continue to lose fat reserves even if the scale doesn't immediately reflect it. By the time you see it reflected on the scale, a good amount of time will have gone by.

Why a good amount of time?

Because a small deficit or surplus (which is what we're talking about when discussing any points above the 2500 level you're angling for and the 3000 level that most estimations would have you at) will not show clearly for several weeks -- which also goes to point out that your level of concern is excessive.

Only you know whether your health risks are higher overshooting or undershooting your maintenance.

From an outside perspective, your level of concern, together with the indication of family concern, says that continuing at a deficit is a higher risk for you.

This is the internet and I'm not a doctor, nor do I play one on TV. It is not THAT difficult to enlist professional assistance these days, what with virtual visits and all!

Assuming you keep your activity constant, eat 3K. See where you're at in a few weeks. Adjust. If you find yourself unable to bring yourself to do so, by itself, this says that getting some help would be an incredibly good idea.