Prometheus: Rules and Query Options?

Hi, everyone

I use Prometheus and would like to use a rule to determine the current value of a metric.
My time interval is 15s. Due to timing deviations, I would use the following query:

rule {instance = “”, job = “node”} [20s]

This means that a maximum of 2 measured values are supplied from the metric. Get the last (current value)I about activating instant.

I chose the format: Time Series and would like to optimize the query options and only
determine and transfer the last 2 measured values.
Which settings would be optimal for the query options?

Query Options ??

Max data point: 2
Min interval: 15s
Interval: 15s
Relative time: 20s
Time shift: empty