I think what you have is either a AXDA2400DKV3C or a AXDA2400DUV3C AMD 2400+ cpu. These would normally run at 133Mhz and with a 15 times multiplier. i.e. 133 X 15 = 2000Mhz. The speed of a 2400+
It would seem that it will only run at the default 100Mhz of the board so this will give you 100 X 15 = 1500Mhz or what you have.
You have either the bios setup incorrectly or possibly a conflict with the speed of memory. Can you post the make and model of the motherboard , how many ram modules you are using and the size and speed of the memory.
Someone may be able to get your cpu running at full speed.