How can I limit number of responses with radio buttons?

I want to use ONE form to offer 15 classes via the radio button. But each class can only accommodate 15 people.  Can I limit the number of responses per radio button in the same field?

Radio button option does not allow multiple selections -- unlike the Checbox.

So, you must be referring to the feature of the Checkbox field instead.

The Checkbox also have the Min/Max Selections option that will allow you to put limits on the number of selection allowed.

Here is a test form http://form.jotformpro.com/form/52155224557959?

You can see the error warning if the Min/Max selection is not followed

You may want to use the Checkbox field instead.

Hope this help. Let us know how we can be of further assistance.

Thanks.