Cartridge Upgrade ...AT ART-9?

Dear @harold-not-the-barrel : The OP 205MK3 are in operation condition but after so many time a change is in order due that the cartridge motor design is similar to the MK4 and any re-tipper only need to change cantilever/stylus with out repair anything else. Even with today boron/stylus will outperform the MK4 and probably its big broter EPC 100C MK4.

As a fact the 205 MK4 and 3 started in the market two years latter than the 100C MK4.b Were the latest MM Technics great designs.

All those are facts to help the OP but if he want to go for the Art 9 is fine with me or even with other MM/MI cartridges.

Other gentleman posted here that the OP needs a phono stage different from what he owns if he wants  LOMC cartridges. At the end it's up to the OP that's whom will " live " with his choices, not you or me.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

Raul, your post was meant to be some other as I never have talked ´bout Technics cartridges. I agree that ART7 may very well be even better than ART9 because it´s very low output 0.12 mV. But it needs a very HQ preamp to get the best out it. For OP it´s better to stay with ART9, first upgrade his deck, then cartridge. Besides, I doubt that ART7 is better than a vintage LOMC say Highphonic in that very low level 0.12 mV. 

Dear @harold-not-the-barrel : My mistake, never mind.

In the other side I still own Highphonic that's very low output a was designed by Denon ex-workers, these gentlemans participated in the Denon very low output cartridge designs and afetr that founded highphonic designing cartridges and a tonearm. Very good cartridges indeed.

The ART 7 is a good cartridge but its sound signature is different from the Highphonic.

R.

The SL-15 uses a p-mount cartridge, of which your choices are severely limited to conical and bonded elliptical moving magnet designs. Keep that SL-15 as it is very historically significant and buy a conventional arm vintage or new direct drive turntable and you will be able to choose from so many cartridges it’ll make your head spin. 

I should add that I own three Technics linear tracking turntables, the SL-DL5 which is direct drive but not quartz locked, and two SL-QL5 turntables, which as the name implies are quartz locked. They use the p-mount system, which is pre-calibrated for any cartridge to work with any turntable. The arm drive on these older units is said to need cleaning and relubrication at the age they are now. This will probably restore some or all sound quality.