Will a Compact Spare fit comfortably behind the front passenger seat?

I've been scouring the forums and have a few unanswered questions.
I have a new '18 Prius Prime Advanced and therefore no spare tire.
I believe if I purchase a 17x4T wheel Toyota P/N 42611-47630 and
a T125/70D 17 tire I'll end up with a compact spare that will fit my car.
Correct?
I want to make doubly sure I need a 17" donut even though the car comes
with 15" tires. If 17" is incorrect I'm back to square one.
I would like to stow it vertically between the rear passenger seat and
the front passenger seat back.
Is there enough space to allow for the thickness of the compact spare?
I do not expect to have rear passengers except on very rare occasions.
Any insight appreciated.
J

 

Based on other discussions here.