A little more privacy when your boyfriend comes over? Ha! I could not even go on my first date until I was 16 let alone even think about having a boyfriend come over.

You want more privacy so you can have sex?  You are only 15! For goodness sakes! What has gotten into this generation.. If I were your parents I wouldn't give you any privacy! Especially at 15. 

i really hate how people older than you (and me) have commented mocking you 'wanting more privacy' because they havent helped atall😂 i would just try and approach the subject in a way that shows them that you understand their point of view, for example saying 'i know you are worried about me getting pregnant, and thats why i want to talk to you about it, so we can prevent it' or something like that?hope that helped :) 

Your 15.. I had to sit in the livingroom the first couple times my bf came over.. Then we couldnt even lay on my bed or floor (still cant) now im not allowed at his house because they found out were sexually active (dating for a year and a half) .. But they did get me on birth control.. But in my opinion, if you keep your kids away from what they want to do, they end up sneaking around to do it anyways.. Your not guna get privacy theyll just laugh at your face. Just because your soster got pregnant at 17 doesnt mean you have to be following her footsteps.. Id suggest some birth control and talk with your parents 

My advice for you would to be open with your parents. If you show that you can trust them by being open with them you might get what you're wanting in the end. Honestly, don't be surprised if they aren't very supportive at first. Like you said, your sister got pregnant at 17 so of course they're going to worry about you with your boyfriend. And you need to respect their decision. It is THEIR house and THEIR rules. If they don't think that you having "alone time" (especially for sex) under THEIR roof then you need to respect that decision. 

Just be honest with them Tell them how well he treats you and that you're trying to follow your heart but you're also being safe

Protection doesn't matter. You're 15. That still leaves two whole years for something to go wrong where you'd end up pregnant. Surely you're smarter than that.