I don't think I've ever paid £15 for a t shirt.
but my children wear a lot of boden. I normally buy it in the sales. I have found little to rival it for quality, tbh.
dd1 had a pair of trousers that she wore for 3 years - she was a portly toddler
, and I used cotton nappies, so needed to buy trousers in a couple of sizes bigger.
bought her a pair of lined cords when she was about 2.6, which she wore until she was nearly 6. 3 years of being crawled in, messing about - lots of rough and tumble, and they were her outdoors trousers for school (SN school, so wears own clothes, and does lots of gardening etc).
and after she outgrew them, they are still fit to be worn and are awaiting dd2.
I bought them for £10, and have never seen similar quality elsewhere - not even close.
Likewise, she has several t shirts which have lasted for years. they probably won't be fit for dd2, but paying £10 and getting a few years constant wear out of a t shirt is not bad value at all in my book.