I have freelanced for 1 1/2 years in munich. Is it true that if caught by the BFA i will only have to pay 10% of my earnings in back payments?

Yes, if you have worked as a freelancer for less than three years (this also includes the time you have worked as a freelancer outside Germany), you can apply to pay half the normal contributions (currently 19.1%), i.e. 9.6%.
This concession is supposed to encourage more people to set up their own businesses here.
If you started working as a freelancer 18 months ago - you can pay pension contributions of 9.6% for three years from the time you started freelancing. If you were a freelancer in Italy, for example, for three years before coming to Germany, you would have to pay the full whack (19.1%) for the whole time you've been here.
How the authorities would check on what you did in Italy, is, of course, another matter.