Is this serious or not to develop swollen feet and legs in 2 week period?

It may be serious. Bilateral swollen feet are usually caused by heart problems or kidney problems related to loss of protein in the urine. Sometimes it may be related to an abdominal pathology or local legs problems. If you have swollen feet please see your physician.
Yes. It can be serious to develop this type of swelling which could be due problems with many different organs such as the kidney, heart and so on. You should first see your pcp.