Pygmy Osprey Standard
I have built and own an Osprey Standard by Pygmy and a Patuxent 17.5 by CLC. You should realize that the Osprey Standard is a 16 foot boat with a multi-chine hull. The Patuxent is 17.5 feet long with a hard-chine hull, but I don’t believe the model is currently available in either plan or kit form. I don’t think the longer boat is any more difficult to carry or cartop and if you have a long enough storage area I would strongly suggest you give up the 15 foot or less limitation. Longer boats can be narrower and are faster. The Osprey is a fairly predictable hull that tracks well and turns sluggishly. I much prefer the hard-chine hull since it is very easy to make rapid course corrections with a little off-side lean; ie, it turns easier despite its longer length. I am 5’ 11" and 180 lb so I’m reasonably close to your size. If I were building a solo sea kayak kit boat right now, it would be the Pygmy Arctic Tern 17. I haven’t paddled one, but have seen a couple up close. I base this recommendation on my preference for a hard-chine hull. If you prefer a shorter, multi-chine hull that tracks well, the Osprey standard is a good choice.
15 foot limit
It is is a storage issue (i.e. the only place you can store it is a space only 15 feet long) then that’s a good reason to stay under 15 feet. When I first decided to build a 17 foot Tern, my boat was 12.5 feet long, and 17 seemed impossibly long and hard to handle. But it is not. My 17 foot tern weighs less than my 12 foot long rec boats. I typically load and unload it myself, while I never turn down a helping hand when it comes to loading or unloading my plastic boats.
If storage space is not forcing you to stay under 15, you should base your decision on other factors, like how you want to use it, etc. My Tern is a great workout boat on big water. But there are times when I wish I had a wood “puttering around” boat with more manueverability for exploring shoreline, small inlets, taking pictures, etc. The Tern is not bad for this, but something like the new CLC Wood Duck might be better.