Graph in Looker Studio with 15-minute interval

[Ruben4]

I have a Google Looker Studio project which gets data from BigQuery. I don't have LookerML. The data is on 15-minute interval, so 4 records for each hour. If I create a graph in Google Looker, I need to choose whether the data is grouped per hour (this results in a sum) or per minute (this results in many empty columns). I have no way to actually set the format of the dimension to a point/column per 15 minutes.

Anyone has a solution for this?