APBH1.5s feature a variety of differences from there forefathers, the APBH1.0s.
A major difference is the memory difference of the two. After reproducing, the APBH1.0 must delete itself, but the APBH1.5 can take simple control of the host before self-deletion. This means the APBH1.5 can control the host AP and move it around. This seems to be useless, but it might serve some use if the APBH1.5 wanted to copy itself in someplace that was not crowded with DPs or AVs.
Another small update is that the APBH1.5 is somewhat smaller than the previous model, allowing it to stay undetected easier. However, most AVs can still detect the virus.