I suspect Erderman is flat rate, like Faulu,so you are looking effectively at circa18%. Stanchart's 10.9% is the best possible rate, which only akina Kirubi are entitled to.
At Mindspeak yesterday Joshua Oigara promised Kenya sub 10% in a year, after KCB float a Euro bond to manage mortgages. A year because the bank has to undergo a credit rating process first.