there's no way you'll ever get 15k for that, especially since the mods are horrendous and it is a sedan (not as sought after). I just sold my 99' hellrot manual trans convertible that had only 77k miles for $13.5k and it was in better condition inside and out with a brand new top and heated and electric vader seats with everything else all original.
I would put it up for around $9k MAYBE, if I was you.
'12 e92 M3 Melbourne Red/Bamboo
- ADV.1 ADV10, Volk TE37SL, OSS, Innotech F1, Arkym, iND
'09 e92 335i Alpine White/Saddle Brown - fully modded