If he hadn't been keen on solids initially I think the reason they said about the 15 minute limit is so that if he's getting fed up or put off you'll have a cut off point and not keep offering food as the longer you try to feed a LO who doesn't want to be fed the more averse they can become if that makes sense!
This is the reasoning we were given as well, only I was told 20 mins. Even now we still sort of stick to that 20ish minutes...not in the sense that he should have eaten a meal in 20 minutes, if he's still hungry and still happily in his chair that is great, but if he is starting to get fussy or tossing food and things and it's been 15-20 minutes I just accept that meal time is finished.
With DS at Finn's age, there were days when he was in and out of his chair in about 2-3 minutes and times when as Shiv said, by the time he ate his finger foods, his stuff that I was feeding him, played with his sippy cup, had a bit of fruit for dessert, smeared it on the tray, rubbed it in his hair, found some bits from the day before stuffed in the cracks and had a go at tasting it, and finally was ready to get out, it could use up a good 30 minutes or more some days!!!
