Heat input for GTAW of 50kJ/in is fairly high. 150 amps, 12 volts, 3 ipm travel gives you 36kJ/in. The important thing with GTAW is that heat input is totally independent from the amount of filler metal that is added to the weld joint. In general, for all other processes, the higher the heat input the more filler is consumed. Actually, you could double the heat input for a GTA weld, without adding any more filler, in fact you could add less.
It is therefore very important that the welder is prudent with filler metal addition. You are using FCAW with Ni and could do the same with the GTAW filler. This would help to assure meeting the required CVN values.