For a starting of $15 per coin we will surely see a lot of dumping. The powers that be behind zcash surely set a high price to give them some room for profits when they start dumping.

"now the question is if we will see a flash dump as soon as it gets on Poloniex. Lots of coins have a similar graph where it insta dumps as soon as it hits the exchange "

We surely will. Almost all of the cryptocoins are dumped the minute they are listed in the exchanges. But the development team of zcash already planned ahead and set a high price. It is overvalued now at Bitmex at .1 BTC.