Then they don't understand it, and you've done a poor job of educating them.

As you say,they didn't estimated yet the risks well enough because lack of knowledge, for big organizations adopting new "open source" technology that no one is responsible for Its a process of years.



There is no "Bitcoin Company" in charge of bitcoin.  Who would you ask for the information?  I'm not aware of anyone making any attempts to record all the fraudulent double-spend attempts or how many of them were successful.  You'll probably need to hire a polling company to do a scientific poll for you.  You could try contacting Coinbase or BitPay and see if they have any internal records they'd be willing to share with you.

There are a lot of analysis tool around the web , like :
https://blockchain.info/double-spends
So maybe there are more specific ones that I am not aware of.



What?  Why would you be any more sure with 4 confirmations than 2?  What's so magical about the number 4?

Maybe I am wrong, but there is a (small) probability that a possible attacker would "hire" couple of miners to "mine" the double spent transaction before the "real" transaction will broadcast to all the network , having 4+ miners who collect that transaction is less likely.(its not must be 4..)
Its a theory, very hard to apply it.
https://eprint.iacr.org/2012/248.pdf


You aren't very good at maths, are you?  If the average time between blocks is 10 minutes, and you want to wait for 4 blocks, it's going to take a LOT more than 6 minutes (on average).  Fortunately, you don't need to wait that long in most cases.

From the 100+ transactions I did,  I never wait more then 10-15 minutes for 4+ confirmations, only when I add very low fee, or even without fee at all..
(I was wrong, its maybe not 5-6 minutes..)



Not sure what you're trying to say there.

That having a bigger block will reduce the wait time because there is more "space" for new transactions,
Its also depends on how the new block size will be synchronized with the miners interactions.