Peer review is generally the most time-taking part of the journal decision making process, and it usually takes anywhere between 2-4 months on an average. In fact, in certain fields, it can take even longer. However, I would recommend that you send an email to the editor asking by when you can expect the peer review to be completed. That way, the editor might also send a reminder to the reviewers and the process can perhaps be expedited.
You can find a template on how to write an inquiry to the journal editor in this article:
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