Hey, I live in england my girlfriend is 16 but I'm only 15 I have been wondering if it legal for us to have sex?;)

Speaking as a fellow Englander, NOPE.
Wait until you are BOTH at least 16 to be legal!!
The LEGAL age of consent is 16 for England.

I just looked it up, and in England, it is 16.

Technically, your girlfriend would be liable for up to 5 years imprisonment is she has sex with you before you are 16.

It is only illegal if she gets caught though.

Source: http://www.brook.org.uk/content/M5_1_consent.asp

I tried to look it up in the statutes, but it kept redirecting me so I used this other source.

And PLEASE be safe.
Use condoms because if not I hope you are aware of the consequences of un-safe sex...