Sudden increase in log_file_sync waits
Log file sync occurs when a commit is made and the redo buffer needs to be flushed to disk. The session has to wait for that to happen.

An increase in the number of log file syncs generally means that one of your developers has gone commit-happy, and is committing far too frequently -- every row, for example.

Here you probably have a process that performs around 1.5 million DML statements with a commit being issued after each one, so look out for some process that loads a few million rows of data.