iPhone 6 (ios8.3) wifi connection keeps dropping every 10-15minute.

My new iphone6 (ios8.3) keeps dropping from the wifi connection. I have my old iPhone 4 using the same wifi connection side by side with my new iphone6, iphone4 is working perfectly. I have reset network connection and even reset all setting, yet, it does not solve the issue. Any idea whether it's a hardware or ios8.3 issue?