How about this....don't deflate your tires. With having that little amount of power, you really don't need to. Also, I agree with Blackbird.....you need to practice more.
When I had my turbo MKIII Supra and first started going to the track with it, I was running high 16's. Then after a couple more times going, I figured out the perfect RPM to launch, and perfected my driving and ran 15.6's all day long. And that's what Car & Driver got out of the car when it was brand new.
Also, this was when the car was 10 years old, and with no mods. And I never did any prep to the car like deflating the tires, just drove there, lined up and ran.