Sauna has regular plug but pops the breaker
Do not upsize the breaker without increasing the wire size, 20 minutes at this overloaded value is about right for most inverse time breakers. I would put the sauna on a dedicated GFCI circuit since water is usually dumped on the rocks / heating element. Is the name plate value is 17a or is this the measured circuit draw? Since the circuit may have lighting included that could be what is pushing you over the limit, with a 16a draw the sauna could be safely powered with a dedicated 20 a breaker and 12 awg wire.