I've heard both the 1.5s and the 2.3s. I owned the 2.3s for about 7 months. Both are great speakers, but the 2.3s are definately an upgrade. The 1.5s are very lively and very space concious (i.e. a small footprint) The 2.3s were much more dynamic however, and presented a bigger soundstage. What does the rest of your system look like?
The 3.6s are also a wonderful speaker, though an older model. You can get a used pair of them for the same price as the 2.3s - probably around $1800.
The 3.6s are also a wonderful speaker, though an older model. You can get a used pair of them for the same price as the 2.3s - probably around $1800.