Hi arslanama,
With a V15, you would have lost signifiant points in ALL 3 major Verbal categories (SC, RC and CR), so you will need to work on more than just RC to hit your score goal. Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so since you've beens studying for just 1 month, it's likely that you will improve as you continue to study. That having been said, you will have to be really efficient with your studies over the next 2 months to hit a 680+. As such, you would likely find it beneficial to invest in a GMAT Course of some type (either Guided Self-Study or instructor-led).
1) How long ago did you take this CAT? If it's been more than 2 weeks, then you should plan to take a new, FULL-LENGTH CAT soon.
2) Did you have to 'rush' to finish the Verbal section of this CAT (and guess on a bunch of questions)? Did you leave any questions unanswered?
3) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich