To my understanding from your POST ,
You are having checkpoint at every log switch ( ONLY ), and log switch is occuring ( 15-18 time )when the redo log is getting filled up. That means you have a big redo size , that will be absolutely OK. Only disadvantage here is your recovery time will be more.
In my DB(s) , i have manged to have 24-30 checkpoints/log switches a day.
Everytime a Log Switch occurs, if your db is in Archive Log Mode then the Archiver Starts and begins to write to the disk.
I've seen terrible performance degradation when doing bulk loads into the databases with smaller log files.
If the OS can handle continuous writes, ie if the Archive Destination is on a separate disk drive, then log switch should not be an issue. It becomes an issue only when logs are switching in terms of seconds. A log switch defines a state of consisteny of a DB.
a). Your recovery time period, i.e. if you want to recover as close to the point of failure as possible. Switching every 5 minutes would be better than switching every 20 minutes. Oracle does recommend every 20 minutes (obviously, every databases requirements are different). And is that 20 minutes during quiet time or busy time.. again this is VERY open to interpretation.
b). You ARCHIVING process, have you enough time to archive off your logs before they are required again.