I have a Subaru Legacy/Outback 2006 model and have the practice of putting new tyres on the back axle and moving the existing rear tyres to the front wheels. That is the practice encouraged by the 'experts' in the TV programme. I've never calculated the mileage done. The worst problem is wearing of the nearside shoulder, kerb side, which I am assured is a problem shared by other 4x4s,

Tyre wear varies between makes, it's a trade-off against grip, ride, noise and other things. But I would expect a lot better than 15K on a set. My present car gets about 35K on a set of four, which I swop around to equalise wear. My old Pug 205 diesel (heavy front end) used to manage about 50K on its relatively small wheels.

If it's wearing the inside shoulders, either you have a really bad front wheel geometry problem, wear or accident damage, or it's more likely caused by straddling speed cushions, those horrible plastic things. If traffic conditions allow, don't straddle them, put one wheel in the gap between them or at the side next to the kerb and ride the other wheel over the middle of the things so that the inside shoulders of the tyre don't take the whole weight of the car at an angle.

As someone with a very light right foot (most of time, though I'm not by any means a slow driver), I normally get well above average for my cars' tyres:

Nissan Micra on 175/60 R13H: ~50k miles on OEM Dunlop SP Sport 200s (bought the car at 21k miles/ roughly 5mm tread, changed the tyres about a year before PXing it [about 7 years of use] when at 2mm on the fronts and about 3mm on the rears). Replaced with Bridgestone Potenza RE720 (little mileage, great tyres though). Tracking done (fronts) when I had the tyres replaced.

Mazda3 gen-1 on 205/55 R16V: ~40k miles on OEM Bridgestone ER 30s (from new) to 6.5 years (3-4mm on the front and 4-5mm on the rears) and ~24k on Dunlop SP Sport Fastresponse at 5.5 years (4-5mm and 5-6mm tread left F/R), replaced by the Michelin CrossClimate + 195/65 R15H earlier this year. No wheel alingment done on this car as not experienced any issues to warrant doing so.

I've only replaced my tyres once due to tread depth - mostly due to age and/or them getting hard and performing poorly in the wet. The last Dunlops were only replaced because they were getting a bit old (grip was fine) but were developing slow leaks due to the OEM alloys corroding, so I thought it was more cost effective (assuming I was to now keep the car for at least another 2-3 years, possibly more) to replace the wheels with (still OEMs) 15in ones that were £65 - £70 cheaper each and get new tyres (I would've replaced them anyway in a year or two [age related]) which were about £10 - £20 cheaper each as well.

It'll be interesting to see what mileage I can get out of the CC+s, given they are deisnged to last a long time and still give good grip when worn (why I bought them, as well as the reasonable winter performance and more cushioned ride on 15in 65 profile tyres). Apparently these are now designed to last at least 10 years, assuming the tread hasn't worn (I normally don't do huge annual mileages).