If the front tires have enough room to turn without rubbing anywhere,
Yes, this is an excellent substitute.
Can you replace 205/65/R15 with 205/75/R15
Yes, you can
Yes, this is a good swap and should work quite well.
no
Your best choices are 205 60 r15.
Yes, they can
No, your speedometer will be off and power and fuel mileage will be adversely effected.
Yes, that is a reasonable substitution.
As far as I know, the different sizes you can fit are: 185/60 R15, 185/65 R15, 195/55 R15, 195/60 R15, 205/55 R15 and 215/50 R15 on the 6x15 alloys. Chris from DIDCOT TYRE & EXHAUST
Yes, they can
Yes, you can