As I know, the KK2.1.5 has been updated to an incredibly sensitive 6050 MPU system. For the price, Naze32 (not full version, full version is much higher) is priced $27.99 on Amazon https://www.amazon.com/gp/product/B01CU4SKS2/ref=as_li_tl?ie=UTF8&tag=rcdronegood01-20&camp=1789&creative=9325&linkCode=as2&creativeASIN=B01CU4SKS2&linkId=6ec903b24dfd3343227b7d08a33d8730 KK2.15 is $14.98 on Amazon https://www.amazon.com/gp/product/B00VI2P39M/ref=as_li_tl?ie=UTF8&tag=rcdronegood01-20&camp=1789&creative=9325&linkCode=as2&creativeASIN=B00VI2P39M&linkId=9675d2983aed9e577cfe258b89b6e2c5