Not able to finish the database creation 10gR2 also the installation fails

 Friends, OS: RHEL As 4.8
DB: 10gR2 (10.2.0.1)

After finishing installation the dbca started when i click the final finish....
DBCA throws the error....

		you <font color="navy">
				<b>do
				</b></font> not have enough free disk space to create the database.
			<br/>you need at least 14738432 KB on /tmp/, you have only 4689920 KB available
			<br/>please allocate more free disk space.
			<br/>
		

i have allocated 5 gb for /tmp ..... is it not enough? am i have to allocate 15 gb as specified above?
also, where will be the mistake?

thanks