Transition wavelengths of 4d-3p, 4f-3d, 5d-3p, 5f-3d, 6d-3p and 6f-3d of Cl XV and K XVII are reported. Corresponding transition probabilities and oscillator strengths are given. These transitions are of potential interest for X-ray lasers with shorter wavelengths towards the "water window". Among them, wavelengths of three KXVII transitions are in the range of the "water window". They are 3p-5d, 3d-6f, 3p-6d.