tires... 30"x9.5r15

[Erebus]

Tire wear depends on a whole bunch of things. Most prominent is the design, performance tires wear out quicker. The basic concept is simple: the stickier the rubber, the quicker it wears. Really hard rubber last long time. But really hard rubber doesn't grip the road as well.

Other factors are alignment and balancing, both front and rear. A wheel that is mis-aligned can wear out in only a 1000 kilometres. Just think, if when you walk, you dragged one foot instead of lifting it, how long would your shoe last? Tire pressure is important too.

That all being said, 30,000 to 100,000 km is reasonable for a tire. Most tires have a "wear rating", and the promotional material will often give some idea.

Forgot to mention this last night: remember that the ONLY thing between you and the road, control and out-of-control, is that small patch of tire that is touching the road surface. So, please don't skimp on tires, get the best you can afford and look after them.

[delicat]

This one isn't about tire brand but sizes. If you're interested to know what is the speed fluctuation or the size difference between the tires you intend to buy and the original then check out this site.
http://www.1010tires.com

I believe the original tires on the Delica in Japan were 215/80R15 which is not available here.

Cheers,
Delicat