The study of gamma-ray blazars is usually hindered due to the lack of information on their redshifts and on their low energyphoton fields. This information is key to understand the effect on the gamma-ray absorption due to either extragalactic backgroundlight and/or intrinsic absorption and emission processes. All this information has also an impact on the determination of thelocation of the emitting region within the relativistic jets. In this work a new optical spectroscopic characterization is presented forthree gamma-ray blazars: S4 0954+65, TXS 1515-273 and RX J0812.0+0237. For all the three targets the redshift determinationis successful, and for the first time in the case of TXS 1515-273 and RX J0812.0+0237. Their classification as BL Lac type isconfirmed based on these new optical spectra. For S4 0954+65 (z=0•36940•0011) an estimation on the disk, broad line regionand torus luminosities is performed based on the observed optical emission lines. The results from this study are compatible withthe nature of S4 0954+65 as a transitional blazar. In the case of TXS 1515-273 (