So what's the minimum number of economic experts necessary for their opinion to be taken as gospel? It's clearly higher than 15 and you have it lower than or equal to 76.
But what about all the other experts who also supported us joining the Euro? They provided their expert opinion too and that's got to count for something. There was Europe 21, a group of business leaders who were firmly in favour of the Euro. Obviously experts in their field. They got it wrong. And then the CBI. A huge organisation crammed full of business leaders, all experts in their field. They got it wrong. And then there's all the politicians, Conservative Mainstream, Labour Movement for Europe and the entire Lib Dems each one numbering in their thousands and in amongst that and especially at Parliamentary level some world-leading experts. They all got it wrong too.
Literally hundreds and hundreds of experts got it wrong over the Euro.
You're engaging in a logical fallacy here. Firstly tu quoque - answering criticism with criticism. You cannot contest the bulk of mainstream economic opinion so you criticise it without actually denying the claim - that Brexit is damaging both in the short and medium-term.
Secondly you assume that because some people got it wrong about the Euro they will be wrong about this, and therefore cannot be trusted. Firstly I find it highly unlikely that there was such uniformity on the Euro question as there is on the Brexit one. I haven't checked the bios of all 100 economists. But by saying that 'hundreds' of experts were wrong before means they will be wrong about a different issue, at a different time, with a different set of circumstances, is frankly ludicrous.
If the Bank of England, broad economic opinion, politicians, EU partners, business leaders, friends and allies around the world say it looks like a duck and it quacks like a duck, it probably is a duck.