Code allows one to use a cordset on a DW and plug it into an accessable receptacle (usually under the sink).
that forms a disconnect.
That is probably the most common method.
But in some areas practice or local amendments require hardwiring.
Code requires a local disconnect.
You can also use breaker in the panel if the person servicing the appliance can "lock" the panel or the breaker to make sure that it stays off.
That is heavly enforced in industrail settings and if the breaker/panel is not locked can lead to injury or death.
In residents often all that is done to put a tape and warning on the breaker.
As to the orginal question. Look at the label on the DW.
If it is less than 15 amps and if the horspower rating (if it has one) is equal or less then the HP rating on the switch then you can use a 15 amp switch.
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