Simplify the following text for a Grade 6 native English-speaking person.
Original: Oates alleged that there existed an extensive Catholic conspiracy to assassinate Charles II , accusations that led to the execution of at least 15 men and precipitated the Exclusion Bill Crisis .
Simplified: Oates said that there was a large Catholic conspiracy to kill Charles II . His story led to the execution of at least 15 men and caused the Exclusion Bill Crisis .