Sure, no appliance case is needed here since the 15″ wide ice maker will simply fit between two base cabinets. Just leave a 15″ wide gap between the cabinets of your choice, and you’ll have sufficient countertop support.
Appliance cases are typically only used at the end of a cabinet run—such as on the end of a peninsula—where extra support is needed to prevent the countertop from cracking or shifting due to regular use, like someone sitting on the overhang.