Practice solving your cross blindfolded, make sure you can plan the entire cross out in your 15 seconds. This is important because then while you are solving your memorized cross solution you can look for F2L pieces to make for little or no pause between cross and F2L.
Make sure you are using at least 10 seconds of inspection in your solves, if you already planned out your cross, great, start planning out where your first pair will be and how to solve it.
Make sure you can look at an F2L case ONCE, and then solve it without looking. During your solves you want to be able to look for your other F2L pieces while you are solving your current one.