Sec. 20. (a) All contracts for construction of an improvement under this chapter shall be let by the municipal works board after advertisement as required for other contracts.
(b) All statutes applicable to the letting and performance of other contracts apply to contracts under this chapter.
(c) The validity of a contract entered into under this chapter may not be questioned, except in an action to enjoin performance. The action must be brought not later than fifteen (15) days from the execution of the contract. If the action is not brought within the fifteen (15) day period, the contract is valid, conclusive, and binding upon all persons.