With an Enterprise
database license, start an additional APW.
As general rule of thumb, if the number of buffers flushed is higher than 10, increase the bicluster size, increase the number of page writers, or increase disk write capacity. For further advice refer to Article:
With a Workgroup
database license, since APWs are not available increasing the BI Cluster size would likely increase the duration of the checkpoints further as the first process that needed to move to a new BI cluster would first have to write all database buffers that were referenced in the BI cluster. Consider upgrading to an Enterprise Database License if performance is a priority.