The 15 seconds are the time you have to activate the buff after you catch a fish. The buff itself stays active until you catch your next fish. So you already have as many tries as you want.

For exmple when you want to catch fish A with a (!!) animation then you use Surface Slap on fish B wich has the same (!!) animation. Now your chances that the next fish with a (!!) animation is fish A are increased - when there are only 2 fish with that (!!) animation in that fishing spot it's up to 100%.
As long as you don't catch any fish the buff stays active. That means you must not catch any of the fish with the (!) animation, just let them eat the bait and try again.