I need another acc fuse but only found one

Hi there,

I have a question here , i am not a car installer so not really knowledgable in this but I am trying to install a fake alarm led. The positive needs to be connected to constant which i found in the fuse box ##21 which controls which is for the front fogs. Now i need to find a acc fuse but i only see one which is already used by my positive wire from my rear view mirror back up camera monitor.
I have a another acc but that controls the Main body ecu ,audio system , shift lock control which is fuse #16. I was told not to fuse tap any fuse that uses the ecu.So now i dont have a acc. I was wondering if i could connect the black ground to fuse #15 which has already been used by the positive wire from the backup camera monitor.There is many empty slots on the fuse box but not sure what the rating would be , for the led fake alarm i would probaly be using a 5 amp since the led dosent use much power.Is that safe , i guess the unused empty slots are for opitons the car did not include. Any suggestions would be great View attachment 57712
Heres is a picture of my fuse box in the cabin. thanks