overoptimistic

adjective

1. disposed to take a favorable view of events or conditions and to expect the most favorable outcome.
2. reflecting a favorable view of events and conditions and the expectation of a positive outcome; demonstrating optimism: an optimistic plan.
3. of or relating to optimism.

adjective

1. excessively optimistic

adj.1845, from optimist + -ic. Related: Optimistical (1809); optimistically.