help with weapon with potion effect cool down

I created a weapon with the ability that, when your health drops to 50% or less, grants regeneration and strength for 5 seconds. However, the problem is that if I get hit again after it activates, it keeps reactivating with each hit. I want it to only activate once and then have a cooldown of at least 15 seconds.

Procedure:

https://imgur.com/a/0lrFX85