Mobil 1 Extended Performance is one of the best oils on the market for street cars (race cars and motorcycles have different requirements and there are oils specifically made for them).  It is a group III synthetic these days in this Country.  No longer a group IV oil made from P.A.O. base stocks.  But still highly refined (though processes such as hydrocracking) and one of the best things you can do to maintain your cars motor in good condition and prevent wear.  Though I would not take for granted that you can automatically go 15,000 miles between oil changes.  If you look at the fine print you will notice it says to observe your manufacturers warranty which will specify oil change intervals (you don't want some damage to be blamed on your not changing the oil at the proper intervals, whether that was the cause or not) and in general says to follow your manufacturers recommendations. There are also typically other qualifiers such as a mileage figure OR once a year. One will notice that there are almost always both a regular and "severe duty" change interval as well.  Many people will fall in to the severe duty schedule so check that to determine the proper change intervals for your vehicle. If one is going to go beyond a manufacturers recommendations after the warranty period hopefully they will have done some research to support such a decision. I would just point out that at the prices this oil is available at it most certainly is cheap protection for preventing wear on your cars engine.  Though the prices I see here are not the least expensive by a long shot.  It is regularly priced at $26.00 for a 5 quart jug at the big retail store that begins with "Wal".  Some auto parts stores like "Azone" will price match so you can get that same price there.  There are also regular sales or rebates on this and other oils which make it unreasonable to purchase it at higher prices since one can plan ahead for something like an oil change. Use the viscosity for your cars requirements and your climate which will also be defined in your owners manual. So getting this high quality oil does not have to be a huge expense, certainly do not go longer between intervals because of cost being a factor, simply purchase it at the low price and change it according to schedule, you can't go wrong there and may be providing yourself an extra cushion which is not necessarily bad either. Of course always recycle your used motor oil and filters, it is free to do at most auto parts stores.  Otherwise I have been using M1 for decades with zero issues of engine wear and I attribute that to careful maintenance with Mobil 1 and a high quality filter such as the Mobil I EP filters that use synthetic media.  High quality synthetic oil that can be purchased at very low prices quite easily in conjunction with a synthetic media filter is going to be a great way to treat your cars engine and a great value as well, this oil accomplishes just that.