BJJ guys are nice enough and they won't bully you for the most part. Kickboxers could be a different story, depending on your gym. They're not like that out of animosity though. Some of the beastly people just have trouble sparring under 50%. I prefer light sparring, because CTE scares me, but when in Rome. I just kind of put out a vibe and react to what I'm given. If you can take a punch to the face, there's nothing to worry about. Don't rely on your chin though. The best thing you could do to make your integration easier is to do pad work outside of class. Pad work is the most beneficial form of training. You're hitting a moving target(or at least you should be) and pre-programming both your offense and defense. You're going to get your azz kicked for awhile, but if you stick with it, you'll find your groove. Joe Rogan used to be a TKD guy. Hew won championships, but got his azz kicked in Muay Thai(which is really American Kickboxing, in most instances). Eventually, he found his groove. He fought in kickboxing professionally a couple times and now he's a 10PJJ black belt. It's worth trying.