After paddling a Delta 12S for several years, I decided to upgrade to a 15S for the added cargo capacity and speed and what a delight it's been. Like it's smaller cousin, the 15S has great primary and secondary stability, good handling and speed, large storage areas and a comfortable cockpit. And best of all, it's lightweight design makes it super easy to load and unload by yourself. After all, what's the use of a great kayak if you dread having to handle it outside of the water.
The only negative I found is the susceptibility of the hull to oil can. Mind you, this was my fault since I left my kayak strapped tightly to my roof rack on a hot day but it's something to be wary about. I also found the deck to be quite slippery for re-entries. More incentive to work on my roll.