Typically, it can take an oven at least 12–15 minutes to preheat depending on your desired temperature. If your appliance is taking much longer to heat up completely, there may be an issue with the airflow or electrical connection.
Avoid lining the bottom of your oven and your oven racks with tin foil as this can restrict airflow and lead to longer preheating and baking times.
Double-check the voltage of your power outlet. An oven installed on lower voltage may take longer to preheat than one installed with higher voltage.
Larger ovens or ovens with additional heating elements may have extended preheating times. Check your product manual for model-specific information.