I have brewed outside for many years, but when I started, I used a gas stove. The good thing about my kettle at the time was that it was wider and shorter, so it could literally straddle 2 burners ( it was an 8 gallon canning pot). So it would come to a boil in about 1/2 an hour or less. Obviously doing partial wort boils your pot would not be big enough to do that. Well hang in there until you can get a bigger pot. You'll be glad you did. Better hop utilization, less darkening, better overall beer. You'll get there.