Thats about the normal operating range of the Nautilus Mini. If I go over 15w I risk getting the dreaded dry hits. If you're wanting to vape more power you'd probably have to go into sub ohm tanks (I have the Kanger Subtank Mini @18W on 1.2 ohm coils). If you do go to a subohm tank I'd recommend a higher wattage mod so you can have some headroom (not running it at maximum). Good luck.