If you use too much complexity, they will see that and will see that you are over-doing it.
If you lose too little, they may think you do not know how to write with anything other than short sentences.
Of course you should not write with one sentence throughout the entire essay, but also do not have several hundred sentences in one page. Let it flow, semicolons will come as they need. If there are only a few semicolons in the entire paper, then let it be; make it as natural as possible.