If you wanted you could fit five in a 15, but I would recommend 4 or 3. I would get more than 2 so the males attention would be divided. You probably know this since you did your research, but make sure the tank is heavily planted, to break their line of sight, cutting down on aggresion. I cant stress this enough! Also, i hope you knwo what your getting yourself into feeding wise, because most dp's(dwarf puffers) will only eat frozen bloodworms. RARELY, i mean very rarely they eat flake, and that is not a suitible diet anyway. Anyway, they re VERY enjoyable fish with so much personality. They coem to teh front of the tank when you walk into teh room, curling their tails behind them.
Also, tellignj between male and females. Males have a black line running down their side, and can fade the line on thier bellies. It is easier thought to look at the "wrinkles" behind their eyes. Females are generally mroe plump and haevb spots all ovver their body.
Avoid puffers with lumpy or sunken in stomachs.
Have so much fun with your puffers and sorry for my ranting. :rant: :duh:
Oh yah, last thing, visit dwarfpuffers.com, its the best website ever for info.
Pufferpeep