You have the wrong cable for that size motor, IGUS has the best cable for these spindles you only need 18AWG for that size motor
1.5Kw Spindle cable can be either of these ( 2 ) Cables
CF6-07-04 ( 8.5Dia 18AWG )
CF6-10-04 ( 9.5Dia 17AWG ) this cable would be Best, but the ( 07 ) will do the job
2.2Kw Spindle cable
CF6-15-04 ( 10Dia 16AWG )
Yes direct wiring using a EMI Gland Shield Cable Restraint is the best of all, see snips