The generator matrix

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

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

Homogenous weight enumerator: w(x)=1x^0+68x^15+748x^16+3460x^17+11388x^18+27692x^19+54475x^20+65832x^21+55220x^22+28252x^23+10967x^24+3060x^25+780x^26+148x^27+49x^28+4x^30

The gray image is a code over GF(2) with n=168, k=18 and d=60.
This code was found by Heurico 1.16 in 122 seconds.