With OpenWRT we can increase the limit, if needed. But it's a delicate process you need to balance out carefully depending on your router. I doubled my slots and it works fine:

It's done via /etc/sysctl.conf

> net.netfilter.nf_conntrack_max=32768

Afterwards "sysctl -p" to apply/ reload the config file. But increasing blindly is a bad idea… it needs to be done with ip_conntrack_buckets in sync for proper balance (memory use, CPU usage). Best to read upon it.

But just going from 16K to 32K shouldn't be any problem for most routers these days.