However, the D2 which does seem to climb well at low speeds seems to
be really sensitive to being towed slow, at least that I understand
from one of the local pilots. Maybe D2 owners could comment on that?

Andy

The D2 also has a very low angle of incidence and thus a high nose
attitude on tow. Could this be part of the issue -- it's just darn
uncomfortable to fly with the nose pointed above the towplane? That
would also account for why 15 meter seems easier. We fly with flaps;
they are interconnected to the ailerons so we're not getting great
roll rates on tow. But it does give a nose down attitude so we can see
the towplane.

John Cochrane