From memory the effective mass of the II/Improved is 6.5 grams (maybe 7.5 - too lazy to look it up) for the fixed head shell version and 9.5 (certain on this) for the detachable head shell version.
Both are excellent choices for the V15 series as is the 12.5 gram non-improved SME arm.
I've owned and used all of them with the sure V15/III (tried the IV, but went back to the III).
I currently use an SME 3009II/non-improved on a Thorens TD125II, though with a Grado cartridge.
The only upgrade I rec for the old SME arms is to have the wiring updated to something better.
DeKay