EDIT: Even with a zero-risk collateralized situation, you would be hard pressed to find someone who would be willing to lend their BTC at an interest rate of 8% for 6 months.
17% per year is a very high interest rate!
Are savings banks give as much?
It's not a lot for crypto lending. Exchanges that offer margin funding (Bitfinex, Poloniex) occasionally get to this APR without you needing to make a 6 month commitment - and the only risk you are taking there is with the platform itself. If the lender is taking on an extreme risk of default, they would want even more interest.