Can i start Group FaceTime with the iPhone 6+

"To use Group FaceTime video calls, you need an iPhone 6s or later, iPad Pro or later, iPad Air 2, or iPad Mini 4 with iOS 12.1.4. Earlier models of iPhone, iPad, and iPod touch that support iOS 12.1.4 can join Group FaceTime calls as audio participants".

Use Group FaceTime on your iPhone, iPad, and iPod Touch

You're welcome. Sorry it's not the answer you we're probably hoping for, but at least you can join as an audio member.