3500$ for 115MH? This is why I don't like high end GPU for mining, if your ROI is  your first target you need to go for smaller GPUs, with just 3600$ I help someone build 240MH mining rig with 10x gtx1660, I think this is the cheapest rig I've ever build... Anyways nothing spoilt your ROI will only take longer unless bull market erupt once again.