I can work in both liter or gallons. 3 gallons = 15 liters.
If it was my grow i would defo move in to the 3 to 5 gallon range and mix your medium with perlite and clay pellets at the bottom of the pot for air and water to easily seep through. Moving in to these size pots wont increase the size of the plant too much but it will increase yield. in the size you have you may well get a few ounce but because of the small pot that might be it. Rule of thumb is that the more medium you have the more yield too. You may end up with a 4' foot plant tho. You could always take some clone and cut them down a bit or you could lst super crop to keep the plant lower.
hope this helps mate.
I'll be watching...
dan