At all times, shared use of existing tall structures (for example, water towers, multistory buildings, church steeples and farm silos) and existing or approved towers shall be preferred to the construction of new towers. As part of the application to install a new telecommunications tower, the applicant must demonstrate that collocation on an existing tall structure is impossible and that the tower is a public necessity in that it is required to render adequate service and that there are compelling reasons, economic or otherwise, which make it more feasible to construct or modify the proposed telecommunications tower before construction of a new tower will be approved.