Unless you are very strong, and lifting like over 30# for dumbell chest presses, I don't see how you can do 15# on kickbacks (an isolation move) and just be using the triceps.
I don't particularly like kickbacks, because I don't think they give a lot of bang for the buck. Bodybuilders use them for shaping and 'finishing off' the muscle, but you've got to have a muslce there to finish off for them to work the best.
I prefer lying extensions (lie prone, with arms towards ceiling, and lower your hands towards your forhead (these are sometimes called "skullcrushers" when done with a barbell, but don't take the name literally!;-) ). You can do them with a barbell or with dumbbells. You can usually lift heavier with a barbell, so that's good for the first set, but I like to use dumbbells for some sets at least. Not only can you change the hand position (palms facing forward or towards each other) but you can add a twist (start at bottom with palms facing in, then turn them to face out at the top of the move) to engage more of the tricep muscle (since the triceps have three functions: to straighten the elbow, to pronate the hand--turn it to a palms-down position; and to help lift the arm behind the body).
Another move I like is a 1-arm overhead extenstion at an angle. Sit so that you are leaning towards one side let's say left). Hold a dumbbell in your right hand, and perform a 1-arm extension. I find that on THESE I can use 15# dumbbells and they isolate the triceps nicely.
There are also 1-arm tricep push-ups done while lying on your side, or triceps dips.
And if you do boxing/kickboxing, the punches help tone the arms.