The L1505 switches are parallel/series, Passive/active with treble boost.
Stock, the L1505 does not have active without treble boost. Also the L1505 treble boost is at a higher frequency than the treble boost on the L2500.
I had a modification done to my L1505 that changed the treble boost to that of the normal active mode (no treble boost) like on an L2500.
My suggestion would be to get the L2500 because it is more versatile. Unless you happen to play the L1505 and just absolutley love it. If you decide on the L1505 you might want to shop used. I got mine used in ex shape for $600
This thread has lot's of little tidbits about the L1500/1505
L-1500/1505 discussion/appreciation thread