When my meningioma was first discovered and measured the size varied slightly when a repeat MRI was done at a different medical center a few months later. The neurologist said that didn't mean it had grown, but could be a variance in the way the second radiologist read and reported on the scan. I've been told benign meningiomas grow about 1 mm-2mm a year. Going from 1.5 to 3 centimeters is a substantial increase in a week's time. Surely the doctor who ordered the scan can offer you an answer. Hopefully you have an appointment in the very near future with the ordering physician who can guide you in the right direction of what to do next.