@Maxine11 Normal use of an oven causes the buildup you describe - it's not necessarily indicative of the guest abusing the appliance or cooking some crazy weird food like "pork." To hit guests with a penalty for making a pretty standard use of a listed amenity would go down very badly.
Perhaps the best solution here would be to either hire a more competent cleaner, or to supply your housekeeper with appropriate oven-cleaning supplies and extend their cleaning time to finish the job properly. It doesn't take a special pro skill to get an oven looking clean, it just takes more than a lazy wipe-down.
Alternatively, if you find that most guests don't require use of the kitchen, you can make it an add-on amenity and ask that guests pre-pay for the additional kitchen cleaning via Resolutions before arrival. This wouldn't be my first choice, because it gets complicated if people change their minds during a stay. Also, since you foreground the word "luxury" in both of your listings, your target customers will naturally prefer all the amenities and cleaning to be inclusive, rather than RyanAir-style add-ons.