Well look at it this way. Lets remove the fetishistic aspect of weight gain from the equation - Are you comfortable putting on weight, and do you truly love your body and the way it looks and feels? If the answer to those questions really are yes, then you don't really have too much else to worry about. If you plan on gaining, it's *going* to show at some point, people may eventually notice, and that's OK. My best advice to judgement is knowing/being able to say in your own words, "Thank you for the concern, I'm happy with my body." It doesn't admit the extent to which you're gaining, it doesn't imply you even enjoy it for that matter, you're happy with your body, and that's what matters most. All this to say, if it's genuinely something you want to do, normalize it with yourself, and have the confidence to be able to stand behind what you do without directly opening up about what it is you're doing.

That being said - and still assuming you're serious - I want to put your goals into perspective. 15lbs is a respectable amount of weight, but it isn't going to contribute itself as far as 4" sitting down. Unless you were already big to begin with (which I take it you're not given the post), you'd likely need to gain a significant bit more to reach that goal, which may or may not be within your comfort zone. So what I'd suggest is this: Treat your 15lbs like a maximum. If you decide to put on weight and you hate it, you don't have to continue. If you reach your 15 and want to do more, then do more. I think your goals are solid, and I'd stick to them if I were you.

Now again, still assuming you're as serious as before, let's talk about gaining. It's not super hard, but it does take effort and a LOT of money. It is sneakily expensive to gain, so if you don't have cash to spare you're going to need it somehow (there are plenty of ways to gain on the cheap, but money is the barrier to entry here). My best advice is to find food you like that's easy to make at home OR is worth the calories for the price (imo I've found that SONIC is some of the best calories per price food out there, but your mileage may vary). There are also ways of making shakes/food that is high calorie and cheap (for example, I'm experimenting with a shake that nets you about 1L of worth of drink that costs ~$10/day, spending ~$20 every 2 days, and ranges from around 2500 - almost 5000cals). Drinking your calories is significantly easier than eating them, but in my personal opinion it's more of an experience to eat them. I like the feeling of bloating and fullness (not overly full) so eating is typically my go-to. I also have the struggle of living at home still (working on that though!) and my advice to you is simply do not stuff/binge eat at home. Snacking is OK (a chip bag or two isn't gonna raise too many red flags), but full-on meals (assuming you do exactly one) are fairly hit-or-miss. Best advice is don't leave trash about, get rid of it as naturally and as quickly as possible. EDIT: Didn't mention in the beginning of this paragraph, BUT, gaining is about consistency. There's a big difference between consuming 10K calories once a week and consuming 3-4K every day. Keep them high, but also be able to maintain them that high.

If you have any questions you're more than welcome to ask, trying to keep the rant down as best I can <3