I don´t mean to be cruel, but that tank is a disaster in several ways....
Way too small for 15 paddletails, no strong current, barely a hiding place, waaaaaaaay too much substrate (and a bad choice of substrate too)...That´s simply not going to work.
I honestly don´t know what to recommend....the way i see it you´ve put yourself in a very complicated situation that has no easy solution. I would separate the paddletails in smaller groups, but that can mean having 5 different containers, which probably shouldn´t be smaller than 60l each. You also need to have at the very least one decent hiding place per animal, plenty of visual barriers and a good, strong current.
The substrate is a hazard as it can be swallowed and it also looks like it´s a bit sharp. Fine sand would be a much better choice, or even better (for feeding and cleaning purposes) no substrate. Also, the substrate should be no deeper than an inch. The way you have it it´s going to cause serious trouble sooner or later as the deeper areas become anoxic and anaerobic bacteria start to flourish.
I´m sorry to be so negative, but you really need to change things.
This is probably not what you want to hear but your chances of ever breeding them are almost non-existent. Very, very few people ever succeed in getting females to lay eggs, and of those people, no more than a handful wordlwide succeed in hatching them and rearing the larvae. No one i know has ever succeeded in raising them to adulthood.
It´s a very difficult species to breed, even more so to raise succesfully. With your current situation, you can forget about it, they won´t breed.