How best to handle consolidating data

Hi all, I use a 1.8 OSS InfluxDB instance to store some metrics ( bandwidth/CPU/MEM) for ~20k machines - about 3metrics per machine, the metrics are logged every 5mins. Tags are used to allocate into Datacenter,Department and Userid

Typically this data is queried only for a single machine at a time in Grafana, using filters on Datacenter, Department and then the Userid. This shows lovely graphs.

This data has been collecting now for ~2yrs. Ive not implemented continuous queries ( basically as ive not invested time in learning/understanding this )

Now i want to use this valuable data to generate a graph at the department level, this works by simple removing the filter on the userid , but is a lot slower and consumes more cpu/mem on the Influx DB, so im here wondering what is the best way to speed this type of query up??

Do i create a new influxdb and run an external script to read all the values for each time window, AVG them and write them to this Influxdb?

Or is this what Continuous Queries give me?

Thanks for reading!