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Acceptable medical insurance for a schengen visa must meet following criteria:
Medical coverage of at least Euro 30,000 (valid in all schengen countries) Must cover emergency medical evacuation and repatriation of remains.
However some embassies/consulates of Schengen Countries requires a "grace period" which will be added to the validity period. This means that 15 days will be added to your visaβs validity. Please note, that validity period and duration of stay is not the same. An example: if you in your application form applied for a 8 days visa, you will always be given 15 days of grace, in total 23 days.
And answer to your first question Does hungary follow the same rule of additional 15 days?
The best answer you can get from Hungry Embassy/Consulate at your home country.
Moreover not all Schengen countries applies this requirement and you have already made 23 days travel insurance, doesn't matter Hungry requires additional 15 days or not it should be acceptable.It will not be a problem.