Caravan tyres

Our 2016 Sprite Alpine 4 van has just been in for its second service I have been advised to change the tyres as they are both cracked around 1cm away from the rim. The date code on the tyres is October 2015, the van is used quite often and has not been left for more than 2 months and the pressures are checked every time it moves. I would have thought they would have lasted more than 2 years or is this normal. Does anyone know whether its best to go back to the dealer to get them changed or take it to someone like ATS.