www.ncbi.nlm.nih.gov/pmc/articles/PMC2936436/Here is real life experiment with a modest sample of 18 people who ate a bunch of fast food to intentionally gain weight for science. I personally find this very hot to just read for fun but you might find it genuinely helpful. On average participants' BMI increased from 21.8 to 24 during the pigging out phase. When they went back to normal life, they initially lost about half the weight they gained, but by two years later they were almost the same size as their fattest, which was still not overweight.
This suggests that yes, gaining 10-15 lbs is likely to shift your set point up a bit metabolically. If you want to go back to your starting weight and maintain that long term, you might find that harder to do. It's also likely that there is some selection bias here because the only people who would consent to be human subjects in a fattening experiment don't mind the idea of gaining weight. So maybe the people in this study either intentionally kept the weight or just didn't really try to lose it.
On the other hand, if your concern is harm to your health as opposed to being just a bit thicker than you started, it's probably not a huge difference but everyone is different. No matter your size, you can try to stay active and eat lots of plants and minimal sugar.