ISO 14001:2015 requires that an organization determines its compliance obligations and keep them updated (clause 6.1.3). ISO 14001:2015 requires that an organization periodically evaluates its compliance obligations status.
For both of these activities, ISO 14001:2015 does not recommend any particular frequency. It is up to each organization to determine the most suitable frequency. Some economic sectors and some countries are more prone to legal changes than others. Each organization determines its frequency and can evaluate its effectiveness by checking if between consecutive determinations many changes are found.
Besides these clauses, ISO 14001:2015 requires that an organization audits its environmental management system at least once a year (actually, ISO 14001:2015 does not set the yearly requirement, the early requirement is set by the certification bodies in their contract with organizations.