I have heard that there is a weight limit of 15 kgs for the pushchair part of the travel system.
Please can you confirm if this is the case or not?
Well, yes, the seat is up to 15 kg (the bassinet up to 9 kg of the baby), so you heard right - 15 kg is the usual European norm, and actually rightly so (a 3 years old is about 15 kg, normally). If the basket is empty, the frame should be able to withstand a bit more, but for that reversible seat, you won't fit a 15+ kg child anyway, so I wouldn't really take that as a problem. The pram is sturdy enough.