We analyse new optical observations of the gravitational lens system SDSS J1515+1511 .
These include a 2.6–year photometric monitoring with the Liverpool Telescope ( LT ) in the r band , as well as a spectroscopic follow–up with the LT and the Gran Telescopio Canarias ( GTC ) .
Our r –band LT light curves cover a quiescent microlensing period of the doubly imaged quasar at z _ { s } = 2.049 , which permits us to robustly estimate the time delay between the two images A and B : 211 \pm 5 days ( 1 \sigma confidence interval ; A is leading ) .
Unfortunately , the main lensing galaxy ( G1 ) is so faint and close to the bright quasar that it is not feasible to accurately extract its spectrum through the GTC data .
However , assuming the putative redshift z _ { G 1 } = 0.742 , the GTC and LT spectra of the distant quasar are used to discuss the macrolens magnification , and the extinction and microlensing effects in G1 .
The new constraints on the time delay and macrolens magnification ratio essentially do not change previous findings on the mass scale of G1 and external shear , while the redshift of the lensing mass is found to be consistent with the assumed value of z _ { G 1 } .
This is a clear evidence that G1 is indeed located at z _ { G 1 } = 0.742 .
From the GTC data we also obtain the redshift of two additional objects ( the secondary galaxy G2 and a new absorption system ) and discuss their possible role in the lens scenario .