increasing font size hangs the emacs

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Hi

I am using emacs (21.1) under X server (fvwm ) environment where I
connect to the X server using vnc client. Running emacs results into a
new X window where fonts are very small. This has started when I
sytared using a computer with high resolution (1440x900). When I
increase the font size  to say 9x15, it takes quite a lot of time to
do this. It gives an illusion of emacs getting hung. Please help. Does
anybody know of a quick fix ?

Thanks