Audio Research LS-15 vs LS-16

If you can plug in an AC cord, you can change tubes.

I've had the LS15 in my system, and the LS16 I've owned. There is probabably a 10% improvement in the 16 over the 15 in stock condition. If you upgrade tubes, you'll et better results with either FOR CERTAIN. The 16 has a bit more room for potential better sound, but not by much. The 16 has the advantage of ALL of it's inputs being pure dirrect for sonic purity, while the 15 only has one input that sounds best. I would pay more for the 15 I guess. However, I find, with the right tubes, you would do with similar results if you just found an old used LS2, 7 or 22 or something like those.( I think that's right). The 22 being best I think. Most of these preamps are in the same sonic ballpark, and you'll have to move to other brands, or the Ref 1 or 2 for better. For the money however, they are nice preamps. But you must get better tubes(valves)!!!
YOu can reach Kevin Deal at Upscale audio in UPland California(upscaleaudio.com), and he's got the scoop on what's best usually for your tube upgrade choices.
Good luck