I don't think it's a good idea to start a new set of ships, if those ships will look much like an existing line. OPLI Barnard in this case.
I think you should play around with the details and proportions a bit before finalizing the design. Play with the form and shape a bit. Right now it looks like an old elite or frontier ship. Make it a bit more interesting. Look at the front RCS blocks of the Amphiesma for example. Or the gun mount of the Natrix.
Here's what I came up with, based on your model:

I've drew it from memory, so the proportions are a bit different.
15 tonnes is nothing. A fully loaded mig-29 is at the same mass, and it has more slender undercarriage. This should be even lighter. The Amphiesma is only 18t and it's bigger.
Also, one engine should be more than enough for a ship this small, no need for two. Except for redundancy.
And there should be some heat radiators on it. Nothing elaborate, just a visual nod towards the heat problem. Again, check Amphiesma or Pumpkinseed for example.
There's an art style guide in the works right now, you can check the
first draft of it in it's thread, and also a draft of an
article about ship parts which might be useful.
Oh, and
here's a guy exported from makehuman. It could be useful for size comparison.
And you should consider learning the new blender interface, the new functions will make your life a lot easier in the long run. Like when it comes to LOD-ing or even UV-ing. You can do two levels of LOD in about two hours without even touching the UV-s, without any remodeling.