Weakaura custom text help

So I’d like to create some custom text for a weakAura but i don’t know ANY Lua.

I’m trying to get a timer to start once the aura is triggered (unrelated to a an actual aura, just once the trigger is met and the WeakAura appears). I’d like the timer to start at 15 and count down to 0. Is there anyway to do this?

The trigger basically just says to show an icon if one of my spell abilities has a CD of >= 105 seconds, but i can’t find a way to get text to print as a countdown from 15. It only starts from 120 and goes to 105 when the WeakAura becomes inactive.

Any help would be much appreciated, I’ve been trying for an hour and haven’t been able to find anything that works online, even the work-arounds don’t seem to work for me.

Thanks