What is the best strategy to prepare for GMAT in 1.5 months?

For Verbals - Go through the OGs

If you have time, for
CR - Go through extra sets example- Aristrotle, MGMAT guide
RC - also go through more practice material example - Aristrotle

Having finished MGMAT Guides, I can tell you that these books will BUILD YOUR FUNDAMENTALS that are very essential to do well on the GMAT. These guides take time but then again, that's the whole point! You should spend the maximum amount of time on your fundamentals. Instead of practising 500 questions, spend the same time going through the books, perhaps twice.

So finish off those books. Then practice timed chunks of questions in OG 12. Practice, say for example, 20 problems with 30 minutes on the clock. That is how you train your mind for the GMAT.

I see you have taken the GMAT, perhaps there might be some apparent holes in your skill that we might fill to get you that score you desire. So post the areas that you feel you are weak on!