I don't know about either the 150mm, the Kento 2.0 T/C or a focus light. It appears that the minimum focus distance advantage of the 150 is offset but the longer lens so the actual working distance at 1:1 is about the same as the 105. (Someone check me if I am wrong.) I have also found that a good number of macro subjects like Pigmys and Blennies react to a focus light and either leave or turn away. The 105VR focuses much faster than the Sigma 150 and goes to f/32 as opposed to f/22 for the 150. I also did not find that the Kento 2.0 T/C worked very well with the 105 even topside.
My solution (on a D-300) is a 105vr with a +10 sub see so I suspect that adding a Nikon 1.7 or 2.0 T/C would be about the same on a modern FF that autofocuses better than my D-300.
I have a Sigma 150 and plan to use it mostly for subjects that won't let me get close enough as opposed to using it for 1:1 or super macro and I hope I will get equivilent supermacro shots to the 105/subsee.
Tom
PS: When shooting Pigmys I have my dive buddy shine a small flashlight on the subject from behind. This illuminates the subject enough for me to find it easily in my magnified viewfinder and causes the Pigmy to turn away from the light in my direction.