Yes, but changing tire size affects driving characteristics, fuel economy, and speedometer accuracy among other things.
Yes, you can substitute the 205/75-15 for the 215/70-15.
No, a 205/65-16 is 1.18" too big in diameter. Your speedometer will read 57.3 at 60 mph. The vehicle will not handle or ride as it should.
Yes, you can.
Normally. yes.
205/60R16 or 215/55R17
Yes you can
215 65 r 15 or 205 60 r 15
NO, the rim size is incorrect.
NO, absolutely not. Never, ever, mix tire sizes on the same axle. You could put a set of 215 on the front and then a set of 205 on the rear but not a 205 & 215 on the same axle. Tires on each axle must be the exact same size.
Yes, that's a reasonable change.
Yes, they are only slightly different.
Yes, they are compatible as a replacement