AR750S-Ext Logging & Cron Levels

When you go into Luci and select System → Logging you are able to set the levels for Log Output Level and Cron Log Level.
Log Output Level - Debug, Info, Notice, Warning, Error, Critical, Alert, Emergency
Cron Log Level - Debug, Warning, Normal

I currently get log entries every 15min when the DHCP refreshes from my ISP, as follows:
Sat Nov 13 00:40:58 2021 daemon.notice netifd: wan (11944): udhcpc: lease of IP address obtained, lease time 1800
Sat Nov 13 00:55:58 2021 daemon.notice netifd: wan (11944): udhcpc: sending renew to IP address

What would the Logging or Cron settings need to be to only show log entries when something not normal happens ??

The log comes from application which control its own log levels.

The log you posted is from netifd. You can refer to some post from opewrt Enabling netfid debug output - #4 by jow - For Developers - OpenWrt Forum