What does the 'V' in the tire size 205/70VR15 stand for? I have a '88 Jaguar XJ6. Can I replace these tires with 205/70R15 without the 'V'? Also how can I or is it easy to replace the 15" wheels with 17" wheels? Thank you very much for your time!

V is up to 149mph. You should never go "down" a rating on the basis of "I never do that speed" because the rating takes into account lateral forces induced by cornering.

See link for full range of speed ratings

http://www.blackcircles.com/general/speedrating

You maybe able to change the 15's for 17's but only by reducing the tyre profile (in your case the 70) but need to be aware of hitting the bodywork.

Speed Rating Mile/Hour Kilometers/Hour Speed Rating Miles/Hour Kilometers/Hour N 87 140 U 124 200 P 93 150 H 130 210 Q 99 160 V 149 240 R 106 170 Z 150+ 240+ S 112 180 W 168 270 T 118 190 Y 186 300

Speed Rating Mile/Hour Kilometers/Hour Speed Rating Miles/Hour Kilometers/Hour N 87 140 U 124 200 P 93 150 H 130 210 Q 99 160 V 149 240 R 106 170 Z 150+ 240+ S 112 180 W 168 270 T 118 190 Y 186 300