I respectfully disagree. The BTC network is a bit slow but that is a known factor and NOT the cause here.
THe cause here is the changelly system is issuing coins, THEY DON"T (yet) HAVE. They should be waiting for any incoming BTC to be confirmed before spending it, period.
Mine was literally 16 transaction deep before I found confirmed coins, all those had to be confirmed before it got to mine. In the mean time, double-spends are of course possible so it's just a bad method to use when you chain up 16 deep pending transactions, no wallet software will let you do that, most won't even let you do it 1 level deep until there's at least 1 confirmation on the incoming coins your trying to spend. That is FAULTY SOFTWARE.
Perhaps it worked great when there was far less transaction in the bTC network, but, come on, scale your crap so it functions, and by all means, don't give people the false impression they'll have their BTC "in 30m" as their estimator said when I initiated the transaction, and STILL says it now, when they are running 1-2-3 I've even hear of 5 days behind. If they had any reputible practice happening, they'd have stopped taking any new BTC (at least outgoing) transction until they clear they're backlog. RIght now they are in a tizzy, many of their real transaction are falling off the back waiting 5 days, miners won't pick those, they have to wait till nodes stop relaying them and re-issue them, a complete mess. I'd surmise changelly is responsible for a good percentage of the perpetual 200k mempool transactions.