About to purchase my new IS250, and recently read that the tires need to be replaced every 15,000 miles.Is this necessary?How much are you paying for your replacements?

The IS250 is a pos. At least get the IS350!

It all depends on the wear of the tred. You need to replace your tires when you get below 2 or 3 mm. When you take it in for service they will look at your tires and give you a good idea how much life you have left in your tires. As far as cost it all depends on what tire you want to get. Just keep in mind when your buying tires, its that only part of your car that actually touchs the road so it may be worth it to invest in a little better tire.

Tires do wear out quick on an IS 250. A lot depends on how u drive the vehicle & u need to make sure u keep them at the proper inflation. The IS has larger tires on the rear, so they can not be rotated, which causes them to wear quicker. However most of the tires I've replaced on an IS have been at 20,000 - 25,000 miles. Cost will vary on tires by brand & the rear tires will cost more than the front tires since they r larger. But u will probably be looking at at least around $1000 for a set of oem tires.