Start by finding how many fish were in the aquarium on the third day 6 * 2 * 2 = <<6*2*2=24>>24.
On day three, Jason took out one-third of the fish 24 / 3 = <<24/3=8>>8.
So at the end of day three, he has 24 - 8 = <<24-8=16>>16 fish.
On day five he has 16 * 2 * 2 = 64 fish, but he takes out one-fourth.
So he took out 64 / 4 = <<64/4=16>>16 fishes.
So at the end of day five, he has 64 - 16 = <<64-16=48>>48 fish.
On day seven he has 48 * 2 * 2 = <<48*2*2=192>>192 fish.
He adds in 15 more, so he has 192 + 15 = <<192+15=207>>207 fish in total.
#### 207