Yes, I think BCH (Bitcoin Cash) is a threat to BTC (Bitcoin) because they share the same resources: miners.

BCH is merely a fork of BTC. Forking open source projects is normal in programming. Some people here say, it just split because of a cash grab. I do not think that's right. It was made because the people behind it just had a different opinion as to how BTC should solve its long standing issues of congestion. The only problem was the BTC community was deadlocked for two or so years unable to move forward. So they just forked/duplicated bitcoin and made the limit change from 1MB to 8MB. This, they thought, was the best option to handle congestion. The rest (those left behind doing BTC) can continue working with their own ideas like Segwit, Segwit2x and/or Lightning Network with the old BTC.  

As a user myself, I find it ridiculous that you have to pay such high fees and wait so long just to get your transaction approved. For a wannabe currency, Bitcoin is definitely not doing a good job at that. Wasn't the point of Bitcoin to become a usable currency? It's definitely crap at doing that right now. But with BCH, you get cheaper transaction fees and quicker confirmations.

For a currency to win, I think it must really give the benefit of being used as currency. When I want to buy coffee with it, I wouldn't want to pay double or triple the price of coffee for my transaction costs and the merchant has to wait for days for my coins to drop into his wallet. To me, the decision is as simple as that. I would bet on a currency project that is catering for user's and merchant's needs.

At the moment, things are stabilizing for BCH. I think there's enough reason to hang on to your BCHs.

If you want more, this article gives a good primer: http://marquezcomelab.com/index.php/bitcoin-network-getting-really-congested-and-time-it-serious-worry