Donut size spare for Prius prime

I don't know. Seems to go quite far back. I think with the front seats all the way back a rear seat passenger would have to be pretty short and have skinny legs Way back in the early Gen II days there were people who made seat mount extenders for the drivers seat to get more leg room. Don't know how safe that would be.

 

Slime 1034-A Tire Plug Kit, 8 Pieces, 9 in L - Walmart.com - Walmart.com

I've done a dozen of these often in sketchy conditions and never had one fail even with also sketchy tires. Its a "life of the tire" repair. I also carry can of "Fit A Flat" to inflate AFTER plugging.

 

The 195/65R15 has a diameter of 25". The Continental Scontact from Tire Rack comes in a T125/80R17 and has a diameter of 24.9". You can use this tire with the 42611-47631 wheel from Toyota Wholesale. They confirmed that the wheel fits a 2022 Prime and presumably any car with a 5/100 bolt pattern. The website has a fitment guide for the wheel - Can't post the website link so google Toyota wholesale direct and search 4261147631 on the website.

Can I just say add that forcing us to jump through hoops to get a compact spare is total BS! Glad Toyota is willing to sacrifice our safety to try to force us to buy a new tire from the stealership.