Panel a: from top to bottom, HIRES RV data for GJ 15 A and GJ 15 B modeled with a linear trend. Blue continuous lines represent the best linear trend model of the GJ 15 A and B datasets, while the red dot-dashed lines show the linear trend expected from the mass ratio of the two stars under the assumption that the other binary companion has the correct trend estimate. Panel b: time series RVs for GJ 15 A obtained with HIRES (green diamonds) and CARMENES (red circles). The fit to the data (black solid line) is a suggestive Keplerian model consistent with a long-period Saturn mass planet on a circular orbit. The dashed blue line represents a third order polynomial approximation to this orbit, which is needed for the statistical analysis (see text). The lower panel shows the residuals to the circular fit. A long-period planet yields a significant improvement over a simpler model fitting only a linear trend.