Well, you really cant hit anything 1.5 times per week without almost doing it twice...right ?
When I do my normal splits I do about 12-16 sets per body part,or 24-32 for the week.
My1x per week nets about 16 sets per body part per week.
I also do a full body 4x per week. With this I get about 4-5 sets per workout in per body part or 16-20 for the week.
So for me, I stay in the 15-30 sets per week on almost all my workouts. (15 being the 1x per week and for me I do powerlifting )
With the particular split we are talking about, I do high volume/low volume. AND high weight/low weight.
I do 10-15 sets for the first workout ,and then on the second workout, I do about 6 sets.
For ME, I need high volume/heavy weights for some body parts, and low volume heavy weight for others, so I do what works for me.(the second workout is mainly just to keep them stimulated and working in different ways, but not overtaxing them)
Also, at weeks end youll be starting shoulders/Legs again and cycling it over.
You ARE touching each parts twice per week really, but not to the extent of your normal volume.
It should fall between your 1xper week and a split as far as total volume.