15 seconds... And the standard for TOTP is 30 seconds. So it's not crazy compared to the standard. Though, there's really no reason for the codes to update so fast.
They are probably doing it to avoid account sharing?
This is the answer here, gyms across the country have implemented nearly identical functionality (bar codes or QR codes are required on entry, staff are trained to be aware of customers sharing or using shared screenshots of the above codes, and the codes have a very short lifetime.)