A certificate under this chapter shall bear interest at such per annum rate as the Secretary deems reasonable, taking into account the range of interest rates prevailing in the private market for similar loans and the risks assumed by the Federal Government; nor may its maturity date, including all extensions and renewals thereof, be later than fifteen years from the date of original issuance. The Secretary may prescribe such other terms and conditions as he deems appropriate. In each case, the Secretary shall consider the feasibility of requiring the railroad to dispose of nonrailroad assets as a condition to a guarantee.