Is the cable from the mic to the keyboard built into the mic? if so there are extensions available and would be easy for anyone with a bit of soldering skill to make if you couldn't find one the right length ready made.
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If the cable is xlr to 1/8" mono the same extension will work but there are also longer cables made to replace the existing cable.
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You should be able to go out to 25 feet with no problems.
If your mic is usb there are usb extensions available as well. If you end up with a length greater than 16 feet (5 meters) you'll need to use a repeater cable.
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As to a smaller room, in general the larger the better.