My best advise is to actually leverage the DEX to your advantage here. So buy into WAVES with the full $15K amount but immediately convert the majority back into USD or BTC or Ether or whatever else you are comfortable in holding in the meantime. Leave perhaps $2.5K in WAVES (You decide, I'm suggesting $2.5K because that's 6 equal splits of your total investment amount) and then gradually buy in as a dollar cost average.
Personally I believe WAVES is a long hold but given the current price spikes and drops with the news I would average my buy-in over time like that just to be careful. But that's my opinion here, feel free to decide what works best for you.