$$ Sheenan Industries has a bond outstanding with $15$ years to maturity, an $8\mathrm{.}25\%$ nominal coupon, semiannual payments, and a $$1,000$ par value. The bond has a $6\mathrm{.}50\%$ nominal yield to maturity, but it can be called in $6$ years at a price of $$1,135.$ What is the appropriate measure of yield to the investor?