I would try to lose the weight, maybe not all of it, but most of it, before TTC. I'm still toting around 15-20 lbs of pre-pregnancy-eat-what-I-want mode, along with some pregnancy weight. I'm working on losing it right now. Like you, I was 150 before pregnancy. That wasn't thin per say, I'm not a thin person, but it was fit and size 10ish for me.
My reasoning to try and lose the weight first is this. While I'm determined to eat right and exercise during my next pregnancy, and I do believe I won't make the same mistakes (eatings bags of Doritos, candy whenever I want etc), if I were to gain 30-35 lbs, starting out at 169 ish (current weight), then I'd be back over 200 when I gave birth, just like I was the first time. And it would take another year to lose 35 pounds of it, and still leave me here, 15-20 lbs overweight. And then I'd have two kids, making it even harder to do the sort of exercise that takes the weight off.
Better for me to get down to 155 ish and then only gain 30-35 lbs, finish the pregnancy at under 200 and hopefully return to pre-pregnancy size. I found the 35 pounds has come off with the breastfeeding, moderate exercise, and relatively lax eating. That tells me that my body was sort of meant to gain that much. But the last 15-20? All me. Bad choices.
That said, I don't think it is irresponsible of you to get pregnant if that's what you really want. But you're so young! You have loads of time. I'm 31 and still don't feel rushed.