In reply to Michael Hood:
DTS is Dry Tooling Style (it's an odd name given that dry tooling using fig 4s is still dry tooling but that's what Jeff Mercier etc came up with). The post above explains what it stands for, though normally when people say DTS they just mean not using fig 4/9 moves.
There is no 'rule' about whether or not you are 'allowed' to use fig 4s/9s. You can do whatever you like/prefer and that might depend on a particular route. Either way will be a generally acceptable ascent, including in competitions. However heel spurs and hooking your leg over an axe (as opposed to over your arm as in a fig 4/9) are out these days as you're basically getting a free rest.
In my experience (which admittedly only goes up to M11, so reasonably hard but a world away from M15), it's not as simple as saying that using fig 4s/9s makes a route easier. It depends on the route and what you prefer. I find sustained fig 4/9 action very tiring as you're basically putting your entire weight on one arm, so if I can DTS and get a foot on to take some weight off or better still get a heel hook, I will generally do that. However DTS often involves long, powerful moves which are hard on your core (probably better training for the real stuff!). So it can be easier in some ways but harder in others.