Marantz TT15/ Clearaudio Satisfy for MC carts?

If you're going to bring your budget up to $6K, then you open up a new set of possibilities.  You could spend a lot less than that and have a much better table and tonearm.  This is a good starting place - Restored Turntables – Sota Turntables

It's a pretty decent table.  I had the Clearaudio Emotion with the Satisfy arm which is basically the same table with a different plinth shape.  It shouldn't have any issues with MC carts so long as you match whatever you get to the arm.  Listen with the Virtuoso before you get ahead of yourself.  It's a very good cartridge.

A lot of turntables that come with a cartridge have "throw in" cartridges, but I would not describe the Virtuouso as a "throw in".  It's a very capable cartridge.  I currently have mine mounted on my souped up Technics SL1200 MK2.  

I would go so far as to say that the cartridge is the best thing about that turntable, followed by the tonearm, with the turntable itself being a little on the cheap side. 

There isn't much mass to the platter or plinth and the feet aren't that great.  The motor can have a tendency to slide around, which will affect speed, or introduce noise if it comes into contact with the plinth.  The power button is on the side of the motor, which sits under the table.  I'm not sure if the TT15 is the same as the Emotion in this regard, but there are two grounding wires, one that loosely attaches under the center spindle in addition to the tonearm wire.  You might not need to use the second wire under the spindle, but if you do it's a little fussy to set up since it connects underneath the table.  

I put a thin sheet of sorbothane under the motor to isolate it and keep it from sliding around.  If you have a surface where it won't slide around, that may not be necessary.  My table came with the Emotion Aluminum Feet (should also work on the TT15), which are very nice. 

The only downside about the Virtuouso cartridge is that the cantilever sticks way out in front of the body and is very easy to unintentionally remove.  When/if you snap yours off, Andy Kim will replace it with a better one and you'll have an even better cartridge.

Nagaoka cartridges are very nice. Having said that, I had a MP-500 and sold it, while keeping the Clearaudio Virtuoso. I no longer have a Clearaudio turntable. Again, I would suggest listening to the TT15 with the Virtuoso and then decide if you want something else. 

I have heard the Mofi Ultradeck, but not head to head with the TT15.  I thought it was a nice sounding deck and appeared to be more straightforward to operate and more user friendly than the TT15.