Topband: Moving the Feedpoint

[Jo,YC0LOW]

I am using a 1/4 w.l. inverted-L for TX on 160 meters. Its ground radials 
bus (consists of 52 wires, between 20 to 40 meters in length) is now located 
nicely beneath the existing feed point on the ground.

But, I plan to to move my tx antenna to second floor (concrete deck) of my 
house. I plan to connect the GND of tx antenna with single copper wire to 
the available ground bus. The distance will be about 15 meters away plus 
elevation about 4 meters high from where it is, now.

What significant effect will the antenna give if  the ground bus is in such 
separate distance, please? I'd appreciate any advices/tips very much. Tnx es 
73 de Jo, YC0LOW