Yes, you can do it.
P205/70r15 95s
The recommended tire pressure for OEM tires on a Toyota Sienna is 35 psi, but you should pay attention to and follow the tire manufacturer's specifications for any aftermarket brand of tires that you purchase.
Yes, by installing 15" wheels.
No, it did not come with them 10 years ago when it was new.
I had a similar situation shortly after replacing all my tires and though the tires were brand new they did not replace the valve stems and they had slow leaks in two of the four tires, this may be your problem. The tire pressure sensors can be very sensitive.
They do not need to be adjusted. Their function is to monitor the air pressure in the tire.
It seems that you need new tires.
Siennas don't have any room for a spare. Toyota provides run-flat tires and low-pressure warning systems instead. Theoretically this gives you 50 miles to drive to the nearest dealer/tire shop/whatever to fix or replace.
Because one or more of the tires is low. If you just had replaced one o more tires, there is need to reset the warning light.
It means at least one of your tires pressure is too deflated. Check the pressure and inflat the tires to the correct pressure and rest the light.
Yes, 215/65R16 tires can work on a 2001 Toyota Sienna, as they are compatible with the vehicle's standard tire size. However, it's essential to ensure that the tires have sufficient clearance and do not interfere with the suspension or body. Always consult your owner's manual or a tire professional for specific recommendations and to confirm compatibility with your vehicle's specifications.
It is possible that your Sienna does not have a spare. Mine was equipped with roll flat tires (RFT) which eliminate the need (in Toyota's mind) for a spare. Saves them a few cubic feet which they can then tout in advertising. i have a 2004 totoya sienna and the spare is under the passinger rear slider door the carpet has a little flap right behind the passinger seat when u open the little flap or carpet there a nut that u turn and the spare will start too come down underneath