An agreement of the parties to a consumer credit transaction with respect to default on the part of the consumer is enforceable only to the extent that:
(1) the consumer fails to make a payment as required by agreement; provided, with respect to a consumer rental-purchase agreement, a lessee defaults when he fails to renew an agreement and fails to return the rented property or make arrangements for its return as provided for by the agreement; or
(2) the prospect of payment, performance, or realization of collateral is significantly impaired; the burden of establishing the prospect of significant impairment is on the creditor.