Maximilian should make the winter sports campaign high priority and the mountain tourism low priority because Maximilian is starting a Shopping campaign for winter sports to sell skis, which are also listed in his campaign for mountain tourism. Maximilian has a specific budget just for his winter sports campaign. When skis are shown, he wants the bid to come from his winter sports campaign.
Explanation: Campaign priority is useful when you’re advertising the same product, for the same country, in multiple Shopping campaigns.
When you have the same product in multiple Shopping campaigns, you can determine which campaign should participate in the auction for that product with campaign priority. Your campaigns already have a priority: Low. But you can change this priority to Medium or High. These priorities determine the bid for any product that the campaigns share.
Read more here: https://support.google.com/adwords/answer/6275296