The 1509 is hit or miss. I ran a 1509 1y on 4s with great success. Really long run times. However, I know others have had heat problems. I have also run the 1512 1.5d and I currently run the 1512 2.5d. The 1509 is noticeably less torquey. However, the power delivery is smooth. You don't have that clear anything with 2 feet of run up power of the 1512, but still can smoke the nitros.

What I learned with the 1509 is that it is highly dependent on the track. It works perfectly for smaller tighter tracks but may not be enough power for larger tracks with bigger jumps and 150 foot plus straights.

The bottomline is I would get the 1512 as you know for fact it will work just fine whereas the 1509 may not work.

IMHO the 1512 2.5d is the most versatile motor for a buggy. Mated with 4s 5000 you can get 20 minutes of run time and run with all but the very fastest of nitros with no problems. Plenty of power. Drop in a 5s battery for a more punchy, embarrass the nitro power band. You can also run 6s with the 2.5d for stupid power.