Why is that number, 'too much?'
What Windows reports is rarely accurate with Java applications.
How much RAM do you have on your machine, and how much was free when your machine started to misbehave?
for example my machine have 16 Gb RAM and SQL developer using ~1 Gb .OS - Win 7
open the java visual vm in the java/bin directory and find out how much memory it was REALLY using
I think it's more likely something else we were doing was causing your performance issue.