How can I make procedure which work for 15 sec?

It depends on what you are trying to do with the item, are you giving the player a potion effect, spawning projectiles, summoning mobs, breaking blocks, etc.

Set a scorbord timer to 300 (20 ticks =1sec) and every tick you can call a procedure taht first test if the timer is counting then do what you will to execute and at the end set the timer -1