Quick answer, very close, if they are perpendicular to each other. Heck, if you are planning that route, you could try a multi-band Fan Dipole, and save on the number of coaxial cables. BTW, the 135ft OCF dipole may do a decent job on 15M. Passing thoughts, especially when dealing with limited space. What wasn´t mentioned is, are you panning to RX only, or RX / TX, with these?