The generator matrix

 1  0  0  0  0  1  1  1  1  2  1  1  1  1  X X+2  0  1  X  X  1
 0  1  0  0  0  2  1  3 X+1  1  X  X  X X+1  1 X+2  1 X+2  2  X X+2
 0  0  1  0  0 X+3 X+1 X+2 X+2 X+3  2  X  3  0  3  1 X+2  2  1  X X+3
 0  0  0  1  0  1  X  3  0  3  2 X+3  1 X+1  0  X X+3  1  3  1 X+3
 0  0  0  0  1  1  2 X+2  3 X+3  1 X+2  2 X+1  3 X+1 X+1 X+1  2  3  0

generates a code of length 21 over Z4[X]/(X^2+2,2X) who´s minimum homogenous weight is 15.

Homogenous weight enumerator: w(x)=1x^0+154x^15+665x^16+1358x^17+2503x^18+3584x^19+5163x^20+5614x^21+5426x^22+3826x^23+2604x^24+1090x^25+483x^26+228x^27+47x^28+18x^29+4x^30

The gray image is a code over GF(2) with n=84, k=15 and d=30.
This code was found by Heurico 1.13 in 3.27 seconds.