You are probably using cheap discs. Do not use cheap discs. Use Verbatim DVD-R Super AZO discs that are manufactured by either Taiyo Yuden or Mitsubishi.
Originally Posted by SoraRoxas
Burning your discs will not cause the games to boot faster directly. Some people have reported things like that, but that is the side effect of their burns being more "correct".
Usually, only older burners, burners with buggy firmware and badly designed burners will have issues with burning discs at fast speeds.
In fact, burning discs at low speeds might even be counter-productive as the discs might not be burned well at all. Some discs were simply not designed to be burnt at low speeds.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit