A 515 is super easy to get in 30 days. As others have said, take a mock.
TTP has a test you can take that helps identify your weaknesses. Focus on just learning the basics of each sub section in each section (DI, imo, tends to be easy once you've studied Q a little) and you can very easily score a 555+. In my experience, I took a little over a month preparing for the GMAT WITHOUT using
TTP and scored 625-645 on my mocks. Because of nerves on test day, try to get 555+ on your mocks since the score I actually got was 595, 30-50 points lower than my mocks (which also had to do with technical difficulties but hopefully you won't have those)