I worked based on my temporary residence and work permit. From 01/04/2020 during the epidemic, my employer closed my workplace. In this situation, do I have to notify the Office within 15 working days, that I have lost my job?

YES - if you were employed in a company, which is currently closed and your contract has been terminated. According to Article 121 p. 1 of the Act on foreigners, a foreigner staying on the territory of the Republic of Poland based on a temporary residence and work permit notifies in writing the Governor who granted the permit, within 15 working days, of the loss of employment at any of the entities entrusting the performance of work, listed in the permit.

This information should be addressed to the Department for Foreigners. If significant circumstances are preventing the fulfilment of this obligation, e.g. illness or the need to quarantine, send such information via the contact form, and send the original by post as soon as you can.