How big of a filter do you have? You may want to consider upgrading sizes. Youll have more options anyway
I keep my endler-X-guppies in a 10, with quite a few more guppies, some killis, a betta, a swordtail and two mollies. Its basically were i put all of my home born livebearers. They do quite well, there is a few aggresion problems. I do have 3 filters on this tank though.
Alot of people on TFF can be really touchy on stocking
Although i do think your tank is a little overstocked

Try to upgrade soon

just one 15 gallon isnt enough for a person's house IMO