You have 3 ways that this can be done.
1. In AUtocad, offset your part geometry by 1.5mm, trim and extend your lines to make sure they end properly, delete the original geometry and program using the offset line.
2. Use additional programming software that takes care of this offsetting for you.
www.sheetcam.com will work. It adjusts the tool path by 1/2 of your cutter diameter
3. Take advantage of the cutter compensation feature in Mach2. This is best used in conjunction with 2. (Not Sheetcam, but some programming software with write a program that utilizes cutter comp) Otherwise you have to add this code manually and this can be quite complicated.