Boyd and Rodriguez Villegas's Mahler measure identity for a conductor-15 elliptic curve

Let $m(P)$ denote the Mahler measure of a Laurent polynomial $P$. Let $E$ be the elliptic curve

$$E: (1+x)(1+y)(1+\frac{1}{x})(1+\frac{1}{y})=1,$$

which has conductor $15$. Boyd and Rodriguez Villegas's conjecture. The Mahler measure satisfies

$$m((1+x)(1+y)+z)=-2L'(E,-1).$$

This identity is presented as an example of the expected relationship between Mahler measures of exact polynomials and special values of $L$-functions, motivated by Beilinson's conjectures and work of Boyd and Rodriguez Villegas. The question mark in the source indicates that the equality is conjectural.