Linn LP 12

You will be far better off asking about Linn upgrades on the Naim forum. 

You would be far better off getting a new turntable. You don't realize how bad the LP 12 is until you replace it with a good one form SME, Basis, Avid, Dohmann or Sota. 

Mijostyn has a clear, consistent, extreme prejudice against Linn turntables before considering, evaluating, or  accepting his advise you might want to read what he has previously posted hear regarding his turntable playback problems he has a lot of them and unusual "fixes" for each one!

@malbor Here is the question regardless of other folks opinions. Do you enjoy this turntable? Do you see the value of these upgrades? 

If yes then do it!

I have an old Thorens TD145 I keep in my system and I love it. Is is as good as my Clearaudio Performance DC 😏 I don't think so but I still love it.  

OP. “Can anyone recommend a turntable that sounds better than the LP 12 for $1500…”

ok, now You asked for it.