Your "15 beat kick" is really a busy kick that is triggered due to lack of balance, very common. It's best to work on refining balance and not be too concerned with the kick at this point. Your priority now is balance
, reducing and quieting the kick. Think easy (not busy) kick and you are kicking in a pool that is only one foot deep. Once you have acquired more balance, you can work on body control and start integrating the kick timing. Although the action and motion of the 2BK is quite simple, it takes a significant amount of balance and body control. When you have more balance and stability, work on the timing of 2BK before moving on to timing of 6BK.
This ad Hoc video was created after an TI Advanced Skills workshop in San Diego at the request of the students in the workshop so they had something to review, compare and contrast in context of 2BK. Kick timing is used to tie in the core and whole body movement, and finish rotation. Surprisingly this demo video has gained a lot of traction at over 40k views, few seem to be critical (can't make everyone happy). In any case this breaks down what the 2bk is, kick timing, swimming with whole body movements: https://www.youtube.com/watch?v=FiPpiC0629I
Happy Swimming, 2BK Kicking, and most importantly BALANCE.