If you are going to use a used miner we can't say if it can mine stable or if it has some defects unless if you buy them directly from the manufacturer.
Also, Innosilicon has some bad support so I don't think it's a wise decision to buy that miner.
About the profitability of 15% per month since we are in a bear market I don't know if you can still get that 15% every month.
Try to contact
offordscott he might be able to help you what is best option to buy.