I think the website only knocks the £15 off when you pick the £90 set - but I would call/email Cobb and ask them. I emailed them a question on a Sunday and got an answer the same day - they seemed very courteous.
I have just had the cob combi plus delivered and it came for £127.50 not quite £15 discount but the man said that the sets had already been discounted. He was really really helpfull and cobb came quickly. If you are going to order and do not already have some heat beads they are difficult to find now because they are out of season. He mentioned to me that for the cost of the fuel and a slight increase in the courier charge that he could send some with the bbq.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.