Subj.
What safe value I can reduce these parameters?
The HOSTIF option is disabled.
That's a lot for an Arduino core
These two values are the size of the transmit and receive buffs for the serial port, which are loop buffs used for buffering in the driver. If hostif is turned off, sending buffs is not used, only receiving buffs are used in the UART driver. Because it is a loop buff, the size can be adjusted according to the actual amount of data transmitted. The minimum value is not recommended to be less than 512.