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.
A big part of why some people choose to go the high end route is that on some older GPUs the efficiency is so low that they cannot turn any profit at all, making them a complete waste where buying Bitcoin alone would be the hands down better option. Buying the higher end cards may not appear worth it at current difficulty and rates, but these things can change a lot. Everyone looks like a genius mining with old ASICs now that were being given away for free 18 months ago, but that isn't always the case. There are so many variables involved in mining, everyone's ideal hardware is different. Same with people's timeframe and risk tolerance. Some people mine with old GPUs until they die, others want to game and resell when it's profitable. You never know what will end up being the best move, but I'm certain it won't be the same for everyone.