Lpc2000

I'm using the following code for the ADC with the LPC2148 and 
Rowley's CrossWorks:

//configuration//
ADCR = (1 << 0)| //SEL = 1, dummy channel #1
 ((15000000/4500000)-1)<<8 | //set clk to 4.5M
 (0 << 16) | //BURST = 0, SW controlled
 (0 << 17) | //CLKS  = 0, 11 clocks = 10-bit
 (1 << 21) | //PDN   = 1, ADC is active
 (1 << 24) | //START = 1, start a conversion now
 (0 << 27);  //EDGE  = 0, 

//Start ADC//
ADCR=(ADCR & 0xFFFFFF00)|(1 << 1) & (~(1 << 24)); //Sets to channel 1
ADCR=(ADCR & 0xFFFFFF00)|((1 << 24)); //Starts the conversion
while((ADDR & 0x80000000) == 0) //get result - adjust to 10-bit 
integer
   ;	
return (ADDR>>6) & 0x3FF;

   
The LPC2148 manual lists 2.44 microseconds for a conversion time (at 
11 clocks) but I'm getting about 44microseconds instead.  I'm only 
writing to an array so I can calculate the a full wave in order to 
calculate the sample rate.  Any ideas what might be causing it to 
sample so slow?
Thanks,
Dewayne