Will alloy wheels with 108pcd and 15 offset fit my ford fiesta mk4, 108 pcd, 35 offset?

The wheels with ET15 are from a Citroen - when tyres are fitted they will probably catch on the wheel arches because the offset is wrong and unless he supplies Ford fitment spigot rings you will get a load of vibration because they won't centre up correctly on the hubs - forget about them - buy proper Ford fitment wheels - you need ET35 with 63.3 centre bore.