We’ll send your Bitcoin within 15 minutes of payment approval or your next transaction is Fee FREE!
Does this mean you'll send a transaction with enough fee so that it will get one confirmation within the next 15 minutes, or you'll send the tx with whatever fee it is within the next 15 minutes?
As a customer, I'd love it if it's the first one.
All it means is that this exchange will broadcast your withdrawal within 15 minutes. If they fail, your next withdrawal is free, which basically means that it can go on endlessly until they actually broadcast your withdrawal.
This is such a lame exchange statement. Definitely not something I would expect from an exchange with 250,000 customers (OP's claim).
Just broadcast your withdrawals right away, or state that you are batching withdrawals so it can take a bit longer because you're waiting for more people to request a withdrawal. Or even better, offer people the option to choose between instant (slightly more expensive) single withdrawals, or batched (slightly cheaper) withdrawals.